polyphase deformation in a fore arc back arc basin salin subbasin myanmar burma the salin subbasin of myanmar part of the larger central basin is a fore arc back arc basin couplet situated between an oblique subduction zone to the west and a major right lateral strike slip fault to the east surface and subsurface expressions of folds and faults suggest that the basin experienced north northwest directed extensional deformation in the miocene followed by east northeast directed pliocene pleistocene transpressional deformation resulting in a variety of structural styles including thrust faults oblique reverse faults strike slip faults and normal faults fault propagation folds cored by west dipping thrust faults in the basin center are located above steps in the top of basement surface most likely fault controlled unconformities at the base of and within the pliocene pleistocene synorogenic section indicate that the thrust faults were active during the pliocene pleistocene the southeastern region contains broad north northwest trending uplifts and east northeast striking normal faults associated with thickened miocene synorogenic deposits pliocene pleistocene sedimentary rocks lie unconformably above the miocene section and are folded above the uplifts reflecting pliocene pleistocene compression in the southern part of the basin miocene sedimentary rocks thicken dramatically over the 20 n uplift and the yedwet uplift suggesting that the north northwest striking faults that bound them represent pliocene pleistocene inversion of miocene normal faults during the miocene the burma plate acted as a fore arc sliver coupled with the india plate subducting obliquely underneath it and moved northward relative to asia along the sagaing fault normal faulting and local basin formation took place at this time when the northern part of the burma plate collided with eastern asia in the pliocene transpressional deformation predominated creating thrust and reverse faults positive flower structures and inverted basins

new insights into the tectonic evolution of the andaman basin northeast indian ocean multibeam swath bathymetry data acquired over an area of about 30 000 km2 together with magnetic and single channel seismic data have been analyzed to understand the tectonic evolution of the andaman basin northeast indian ocean swath bathymetry data revealed several morphotectonic features that divide the basin into a complex western part comprising arc parallel seamount chains and n s trending fault systems and a relatively smooth eastern part a sw ne trending spreading ridge bisects the basin an offset of about 11 8 km at 94 21 e longitude divides the spreading ridge into sw and ne segments high resolution bathymetry and magnetic data enabled us to identify two finer scale segments over the sw part of the ridge that display distinct topographic fabric compared to the ne segment thin sediment cover and presence of axial seamounts characterize sw segments of the ridge whereas the ne segment has thick sediment cover and well maintained rift valley kinematics of basin evolution derived from the identification of the seafloor spreading magnetic anomalies suggest very slow initial opening rates of about 1 6 cm yr and an increase in the spreading rate to about 3 8 cm yr from anomaly 2 to present although this interpretation relies only on magnetic anomalies in the two westernmost segments it is suggested that the true seafloor spreading started about 4 ma in the andaman backarc basin rather than the 11 ma postulated previously we infer based on the integrated analysis of swath bathymetry magnetic and seismological data that the basin has evolved as a consequence of extrusive tectonics that prompted extension and rifting along the plane joining the sagaing and semengko fault systems extension by seafloor spreading during the past 4 myr resulted in the formation of the deep andaman backarc basin this phase has also experienced westward propagation of the spreading center

coupling and decoupling of crust and mantle in convergent orogens implications for strain partitioning in the crust topographic relief strain partitioning and crust mantle coupling within convergent orogens may be systematically related to the distribution of strength as a function of depth within continental crust this result is obtained by solving analytically for basally driven three dimensional flow within an idealized crust with a laterally invariant depth dependent newtonian viscosity two end member flow states are shown to occur in the first crustal flow is directly coupled to the underlying mantle and is controlled by stresses transmitted vertically through the crust in the second upper crustal to midcrustal flow is decoupled from the underlying mantle and is controlled by stresses transmitted horizontally through the crust this model is applied to deformation of continental crust above plate like mantle that undergoes oblique convergence across a narrow suture if no significant low viscosity zone develops within the crust crustal deformation is coupled to motion of the underlying mantle and a triangular mountain range develops surface shortening occurs at the foot of the mountains normal to the trend of the range while strike slip and extension are partitioned along the axis of the orogen if a low viscosity zone is initially absent but develops during crustal thickening a steep sided flat topped plateau forms crustal deformation is coupled to mantle motions on the plateau flanks but may be strongly decoupled beneath the plateau surface shortening normal to the plateau occurs at the foot of the plateau while surface extension normal to the plateau occurs at the plateau edge if a low viscosity zone is present in the lower crust prior to convergence a wide orogen with low topographic relief develops crustal deformation is decoupled from the mantle except at the edges of the deforming region and surface shortening is partitioned uniformly across the belt this study shows that horizontal and vertical partitioning of strain occur even in the absence of lateral strength variations and that shortening and extension may exist simultaneously in different parts of an orogen similar morphology and strain partitioning can be observed in many real orogenic belts including the eastern alps the tibetan plateau and the lachlan tasman fold belt

the evolution of illite to muscovite an example of the behaviour of isotopes in low grade metamorphic terrains abstract a review of the possibilities and limitations of the use of radiogenic isotopes in low grade terrains i e in the temperature range below the blocking temperature of potassic white mica is discussed using a background of a data base of over 500 isotope analyses on more than 250 illitic muscovitic samples published in various papers special stress is laid on the main problems 1 distinction between detrital and neoformed minerals 2 the slow evolution of minerals without pronounced breaks and 3 retention problems of radiogenic daughter products a brief description of low grade metamorphism is given and criteria enabling a subdivision into low to very low grade metamorphism are discussed comprising illite crystallinity mineralogy fluid inclusions and coal rank measurements the useful type of lithologies for this kind of work ranges from shales slates through volcaniclastic tuffs with high primary glass contents and limestone dolomites marbles to mylonites it can be concluded that carefully selected illitic muscovites yield geologically meaningful ages provided that more than one isotopic method is applied

gravity anomalies flexure and the elastic thickness structure of the india eurasia collisional system wehaveusedbouguergravityanomalyandtopographydatatodeterminetheequivalentelasticthicknessofthelithosphere te in the region of the india eurasia collisional system comparison of observed and modelled gravity anomalies along 1dimensional profiles suggest there are significant variations in te along strike of the himalaya foreland estimates decrease from a high of 70 km in the central region to 30 50 km in the east and west we have verified these inferences of spatial variations using a 2 dimensional non spectral interative flexure and gravity anomaly modelling technique the himalaya foreland forms a high te 40bteb100 km rigid block with a well defined edge as shown by the localisation of faulting and deformation along its northern margin other highteblocks occur to the north beneath the qaidam and sichuan basins the tibetan plateau forms a low te 0bteb20 km weak region that extends from the central part of the plateau into south western china tectonic styles in the india eurasia collisional system therefore involve both drigidt and dnon rigidt blocks where high te rigid blocks are present the stylesdominatedbyunderthrustingofthemorerigidblock wherethecollisionalzoneisnotconstrainedbyrigidblocks however the style appears to be dominated by lower crustal flow and a more continuous style of deformation d 2005 elsevier b v all rights reserved

trends and evolution of contamination in a well dated water reservoir sedimentary archive the brno dam moravia czech republic the sedimentary record from dams can provide important information about stratigraphy and pollution history of densely populated river basins the brno dam is a small reservoir within the morava river catchment czech republic accumulating lacustrine sediments since 1940 dam filling the stratigraphy of the dam sediments was studied using multiproxy stratigraphic analysis x ray densitometry bulk magnetic susceptibility diffuse spectral reflectance and cation exchange capacity of five sediment cores supported by ground penetration radar sections concentrations of heavy metals were studied by x ray fluorescence analysis the thickness of the dam sediments decreases from 220 cm in the proximal part near the feeder to only 10 cm in the distal part near the dyke sediments consist predominantly of finely laminated silty sands silts and clays the sedimentation rate for the last 22 years inferred from 137cs dating decreases from 4 2 cm per year in the proximal part of the dam to 0 29 cm per year in its distal part distinct long term trends were found in the depth profiles of heavy metal concentrations the heavy metal contents increase significantly after 1940 in all cores with peak concentrations confined to layers deposited in the 1960s and 1980s a decreasing trend occurred after 1989 the decline in czech heavy industry the results also show that heavy metal contamination is dependent on lithology hyperpycnal flow layers related to floods increased concentrations of phosphorus in the sediments indicate long term eutrophication of the dam despite the recent decreasing trends in heavy metal concentrations the phosphorus contents remain high in recent years and have caused persisting problems with algal growth in the dam mentioned by previous authors

tectonics of the western margin of the shan plateau central myanmar implication for the india indochina oblique convergence since the oligocene abstract we present new data and interpretations on the neogene tectonics of the shan scarp area central myanmar and its relationship with the india indochina oblique convergence we describe ductile and brittle fabrics associated with the major features in this area the mogok metamorphic belt mmb the shan scarp and the sagaing fault from these data we identify a succession of two tectonic regimes first a dominant nnw sse trending extension marked by ductile stretching that characterizes the mmb and associated n70e brittle normal faults later from middle or upper miocene to the present these structures were cross cut by brittle right lateral faults among which the most important are the n20w transpressive shan scarp fault zone and the n s sagaing fault to explain this transition from a dominant transtensive to a transpressive stress regime that occurred during miocene we place our data within a larger geodynamic context we suggest that like the intraplate deformation in the indian ocean the end of spreading in the south china sea the opening of the andaman basin or the end of subduction within the indo burma range the change in the tectonic regime in central myanmar could be in response to a major miocene regional plate kinematic reorganization

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

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

structures uplift and magmatism of the western myanmar arc constraints to mid cretaceous paleogene tectonic evolution of the western myanmar continental margin abstract knowledge of trans himalayan tectono magmatic evolution is critical to understanding the complex pre collisional history of southern eurasia active continental margin it has been proposed that magmatic rocks of the trans himalayan batholith extending from southern tibet to southeast asia are now exposed as the western myanmar arc and central granite belt in myanmar yet origin emplacement and relationships of the two juxtaposed belts remain poorly constrained in this study 2d seismic and drilling data for the western myanmar arc zircon u pb age and hf isotope and whole rock geochemical data for magmatic rocks from the arc have been applied our seismic profiles borehole stratigraphic sequences and zircon u pb data show that a typical arc basin system was well developed along the western myanmar continental margin the magmatic arc has experienced at least three igneous events in the mid cretaceous 110 90 ma latest cretaceous early paleocene 69 64 5 ma and eocene 53 38 ma as well as three associated uplift processes in the late cretaceous eocene and late oligocene whole rock geochemical characteristics and zircons showing variable but predominately positive e hf t values suggest a significant juvenile mantle source involving a proportion of ancient subducted sediments and juvenile crustal materials for these typical arc related magmatic rocks the identification of mid cretaceous to paleogene magmatic rocks having positive e hf t values from the western myanmar arc 1 indicates that the magmatism can be correlated with the gangdese arc within the lhasa terrane of the southern tibetan plateau 2 provides evidence for the proximal derived model that paleogene sediments in the central myanmar basin were from the western myanmar arc but were not delivered by the paleo yarlung tsangpo irrawaddy river system from the gangdese arc and 3 enables a model of eastward subduction of the neo tethyan indian oceanic crust to reflect onset of the magmatism at the mid cretaceous and a long existed back arc extension in western myanmar

diachronous cooling along the mogok metamorphic belt shan scarp myanmar the trace of the northward migration of the indian syntaxis abstract we present new observations and new mineral ages eight by the 40 ar 39 ar and nine by the 40 k 40 ar methods from high grade metamorphic and foliated intrusive rocks collected along the mogok metamorphic belt of central myanmar that complete preliminary results we previously published all 30 ages presented here confirm the oligocene to middle miocene age of the mogok metamorphism moreover the ages are young from the gulf of martaban in the south to the china myanmar border in the north showing a clear diachronism these results confirm a northward migration of the tectonic event responsible for the cooling of our samples at a velocity similar to the india relative to indochina velocity at the same period in addition intensive field work along a 800 km long section of the mogok metamorphic belt has revealed the numerous ductile structures that resulted from a strong nnw sse trending extension from the analogy between the present day local extrusion around the eastern indian syntaxis and the extension observed along the mogok metamorphic belt and from the diachronism we document we suggest that the central part of myanmar has recorded the northward passage of the eastern indian syntaxis with respect to indochina from oligocene to middle miocene

seismological geodetic macroseismic and historical context of the 2016 mw 6 7 tamenglong manipur india earthquake abstract the 2016 mw 6 7 tamenglong earthquake in the state of manipur in northeastern india on 4 january 2016 at 04 35 indian standard time 3 january 23 05 utc was the strongest earthquake to strike manipur since 1988 using data from indian stations we constrain the hypocentral depth of the mainshock at 59 3 8 km and determine a strike slip mechanism with a moderate reverse component on a steeply dipping plane though coseismic offsets from gps measurements from four nearby sites were inadequate to provide further constraints on the focal mechanism they were consistent with the magnitude and hypocentral depth of the earthquake the epicentre of the mainshock was located 15 km west of the churachandpur mao fault cmf but it was unrelated to this structure and was instead a typical intra slab earthquake within the indian plate a strong motion instrument at the loktak power station lok 56 km from the epicentre recorded a peak ground acceleration pga of 0 027g while a pga of 0 103g was recorded at shillong shl at an epicentral distance of 111 km we also present macroseismic observations from 461 locations in north eastern india and the adjacent areas for this earthquake the highest intensities 7 ems were observed in the manipur valley and in the hills to the west while shaking was perceptible as far as delhi and jaipur lastly we present a catalogue of 333 felt earthquakes in manipur from 1588 1 ce to 1955 derived from the royal chronicle of the kings of manipur known as the cheitharon kumpapa discuss important historical earthquakes in the region and also estimate intensity magnitudes for the 1852 mi 6 5 0 8 1869 mi 7 1 0 7 1880 mi 6 3 0 7 and 2016 mi 6 8 0 8 earthquakes

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

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

40ar 39ar dating of white micas from an alpine high pressure metamorphic belt on naxos greece the resetting of the argon isotopic system overprinting of white micas from high pressure low to medium temperature m1 metamorphic assemblages in pelitic schists on naxos during subsequent thermal dome m2 metamorphism ranges from minor in the southeast of the island to complete recrystallization in the amphibolite facies rocks near the migmatites in the centre of the dome the original m1 minerals are phengites si4 6 7 7 0 and the overprinting minerals are muscovites si4 6 0 6 45 40ar 39ar step heating analyses of white mica separates from rocks in the area where phengite and muscovite occur together yield complex age spectra characterized by low apparent ages in the first and the last stages of gas release and high apparent ages in between these upward convex age spectra are shown to be caused by mixing of two generations of micas each of which has a different age spectrum and argon release pattern seemingly good plateaus in some age spectra from white micas of the area must be interpreted as providing meaningless intermediate ages further the upward convex age spectra have been used to trace the isotopic signature of phengites toward increasing m2 metamorphic grade and suggest that as long as phengites can be observed in the rocks upward convex age spectra occur on naxos crystallization of muscovite at the expense of phengite appears to be the main mechanism of resetting argon isotopic ages in white micas however there is also good evidence for argon loss by volume diffusion from phengites simple diffusion calculations suggest that the m2 metamorphism was caused by a shortlived heat source

radioactive production and diffusional loss of radiogenic 40ar in clays in relation to its flux to the atmosphere abstract this paper addresses the release mechanisms of radiogenic 40 ar from clays for the purpose of estimating the 40 ar flux from the sedimentary crust to the atmosphere clays from sedimentary sequences of cambrian to neogene age show discrepancies between their depositional stratigraphic ages and the k ar apparent ages or dates of the different size fractions the possible geochemical mechanisms that may be responsible for the k ar dates being either higher or lower than the stratigraphic age are discussed in general the known observation of a decrease in the k ar apparent age of clays with decreasing particle size is interpreted as due to a faster escape of radiogenic 40 ar from the smaller particles in the younger neogene clays the mass fractions of 40 ar lost are in a range from 13 to 34 in the fine size particles that are smaller by a factor of 10 in their linear dimension than the bigger particles in the older formation samples cambrian to triassic the 40 ar loss is smaller from 7 to 19 for the same particle size range this smaller decrease in the 40 ar 40 k ratio in the stratigraphically older samples may be at least in part accounted for by the closure of the mineral system after the process of 40 ar escape went on for some time in all sediments a lowering of the k ar apparent age of the different size fractions mainly in the smaller is possibly due to authigenesis of mixed layered illite smectite and illite as a new generation of particles that result from and are therefore better adapted to the new diagenetic environment in a neogene basin sediments of depositional age as an overall model we present a mechanism that explains the lowering of the 40 ar 40 k ratio and k ar apparent age in fine clay size fractions based on the production of 40 ar in a closed system for some period of time followed subsequently by the diffusional escape of 40 ar with its continuing production from 40 k in the particles this analysis gives 40 ar diffusion coefficients consistently in a range from 10 28 to 10 27 cm 2 s from the results in this paper the flux of radiogenic 40 ar from the sedimentary crust to the atmosphere is estimated as 5 to 13 10 6 mol year which is about 15 to 40 of the flux from the whole continental crust as reported by other investigators

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

earthquake focal mechanisms in yunnan and their inference on the regional stress field using the broadband records from a regional permanent network we determined the focal mechanisms of 174 small and moderate earthquakes 3 4 m w 6 0 from january 2008 to march 2011 in yunnan china by fitting the three component waveforms of p and s waves results show that the earthquakes predominantly have strike slip mechanisms with occasional normal and very few thrust faulting events most earthquakes occur in the upper crust above 16 km depth we then derive the regional distribution of the stress field through a damped linear inversion using the focal mechanisms obtained in this study and augmented by the solutions in the global centroid moment tensor gcmt catalog and in xu et al 2010 inversion results suggest that the entire region is predominantly under a strike slip faulting regime orientations of both maximum and minimum principle axes exhibit a clockwise rotational pattern the axes of maximum compression are oriented roughly north south with a gradual change across the region from trending northwest southeast in the south china block to trending northeast southwest in the indo china block this pattern is consistent with the surface horizontal velocity derived from geodetic observations localized normal faulting stress regions are observed in the tengchong volcanic zone and in the qiao jia segment of the xianshuihe xiaojiang fault zone online material tables of earthquake catalogs and figures describing stress inversion tests

asymmetry in elastic properties and the evolution of large continental strike slip faults 1 we use geodetic studies to quantify several cases of significant asymmetry in interseismic and coseismic effects along large continental strike slip faults using simple two dimensional edge dislocation models we first show that asymmetric elastic loading characterizes the present main marmara fault a portion of the north anatolian fault along the northern margin of the sea of marmara the ratio of asymmetry there is about 10 this ratio is even larger about 30 along the northern sumatra fault near lake toba caldera we then examine two profiles near point reyes and point arena across the northern san andreas fault that have been previously proposed as affected by asymmetry both in interseismic and coseismic effects we show that an asymmetry ratio of 1 6 in interseismic loading exists near point arena with the southwest side of the fault being more rigid than the northeast one on the other hand we do not find significant asymmetry for the point reyes profile that was previously described as highly asymmetric we examine coseismic motion during the 1906 earthquake along the same two profiles ratios of 1 2 and 1 7 are found for the point arena and point reyes profiles respectively we discuss the possible causes of asymmetry contrasts in seismic velocity in the brittle portion suggest ratios generally not exceeding 2 5 for the dynamic rigidity in the upper brittle section larger ratios may involve other complex causes such as differences between static and dynamic rigidities contrasts in rheology in the deeper creeping sections and postseismic transients we conclude that asymmetry should be systematically included within the parameters to be inverted when dealing with the mechanics of large scale strike slip faults

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

post seismic relaxation following the great 2004 sumatra andaman earthquake on a compressible self gravitating earth summary the mw 9 0 2004 december 26 sumatra andaman and mw 8 7 2005 march 28 nias earthquakes which collectively ruptured approximately 1800 km of the andaman and sunda subduction zones are expected to be followed by vigorous viscoelastic relaxation involving both the upper and lower mantle because of these large spatial dimensions it is desirable to fully account for gravitational coupling effects in the relaxation process we present a stable method of computing relaxation of a spherically stratified compressible and self gravitating viscoelastic earth following an impulsive moment release event the solution is cast in terms of a spherical harmonic expansion of viscoelastic normal modes for simple layered viscoelastic models which include a low viscosity oceanic asthenosphere we predict substantial post seismic effects over a region several 100s of km wide surrounding the eastern indian ocean we compare observed gps time series from ten regional sites mostly in thailand and indonesia beginning in 2004 december with synthetic time series that include the coseismic and post seismic effects of the 2004 december 26 and 2005 march 28 earthquakes a viscosity structure involving a biviscous burgers body rheology in the asthenosphere explains the pattern and amplitude of post seismic offsets remarkably well

state of tectonic stress in northeast india and adjoining south asia region an appraisal an attempt is made to map the spatial variation of the tectonic stress pattern in northeast india and its adjoining south asia region using stress tensor inversion of some 516 fault plane solutions the bhutan himalaya and the arunachal himalaya are mapped with north south to north northwest south southeast compression the eastern himalaya syntaxis zone on the other hand shows a clockwise rotation a north northeast compression is dominant to the south in the intraplate part of the region the shillong plateau assam valley bengal basin bangladesh and tripura fold belt exhibit north northwest to north northeast compression orthogonal horizontal extension is dominant in southern tibet bhutan and partly in the syntaxis zone and the same is also observed in the shillong plateau and assam valley area of the intraplate region the indo burma ranges and the sagaing fault in the myanmar region show a northeast southwest compression an orthogonal horizontal northwest southeast extension is also observed in the sagaing fault zone a depth variation of the tectonic stress is observed below the indo burma ranges it changes from north south to northeast southwest in the southern part and from northeast southwest to north northeast south southwest in the northern part in the deeper seismogenic zone the stress inversion results of clusters of events in individual zones though mostly conformable with the average observations indicate a variation in the shillong plateau due to heterogeneity and tectonic complexity

a comprehensive assessment of ground motions from two 2016 intra slab earthquakes in myanmar abstract we map the distribution of macroseismic intensities from the mw 6 9 kani and the mw 6 8 chauk intra slab earthquakes in 2016 in myanmar using the 1998 european macroseismic scale ems 98 by interpreting data gathered from field surveys community responses sent via social media to the myanmar earthquake committee mec and digital news reports our macroseismic maps for both events provide better spatial data coverage in myanmar india and bangladesh than community derived macroseismic maps e g u s geological survey s did you feel it in myanmar this was driven by improved telecommunication that has allowed social media such as the burmese language facebook portal of the myanmar earthquake committee mec to reach into rural areas from where reports of shaking effects from earthquakes have been previously unavailable our analysis of both the macroseismic intensities and strong motion observations from india and myanmar suggests the two earthquakes had different source properties the comparison of our intensity data with instrumental strong motion records also suggests the peak ground motion intensity relationship by worden et al 2012 generally performs well for both earthquakes in addition ground motion behaviour within the burma and indian plates can be related to different existing ground motion prediction equations gmpes and intensity prediction equations ipes for subduction zones and for stable continental regions respectively we therefore suggest these effects will need to be considered in future regional seismic hazard models or shake maps for this region when evaluating the impact of the future events

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

mineralogical chemical and k ar isotopic changes in kreyenhagen shale whole rocks and 2 μm clay fractions during natural burial and hydrous pyrolysis experimental maturation abstract progressive maturation of the eocene kreyenhagen shale from the san joaquin basin of california was studied by combining mineralogical and chemical analyses with k ar dating of whole rocks and hydrous pyrolysis was intended to alleviate the problem of mineral and chemical variations in initially deposited rocks of naturally matured sequences however experiments on aliquots from thermally immature kreyenhagen shale outcrop sample did not mimic the results from naturally buried samples experiments conducted for 72 h at temperatures from 270 to 365 c did not induce significant changes at temperatures above 310 c in the mineralogical composition and k ar ages of the rock and large amounts of smectite layers in the illite smectite mixed layers of the pyrolyzed outcrop

time constrained illitization in gas bearing rotliegende permian sandstones from northern germany by illite potassium argon dating permian rotliegende sandstone cores were collected from an area of about 14 800 km2 5710 mi2 mostly to the east southeast of the city of bremen in northern germany at depths between 4596 and 5330 m 15 079 17 487 ft the separated size fractions 0 2 0 2 1 0 and 1 0 2 0 m consist of illite 90 100 with small to minute amounts of chlorite and detectable quartz and feldspars in the coarser fractions scanning electron microscopic and transmission electron microscopic observations showed two types of illite morphologies flakes coating detrital framework minerals and laths and fibers invading the pore space the data points of most size fractions fit two isochrons with slopes providing ages of 191 8 and 178 1 ma with initial 40ar 36ar ratios reasonably close to the atmospheric value microthermometric fluid inclusion determinations in quartz and calcite characterize two types of percolating fluids a highly saline 19 nacl equivalent fluid at variable temperatures depending on the reservoirs 185 to 150c and a slightly saline one 2 6 nacl equivalent again at varied temperatures 170 to 145c also depending on the locations these temperatures are higher than paleotemperatures calculated on the basis of a present day burial gradient of 30 5c km therefore favoring hydrothermal illitization with the oldest illite crystallizing at a generally higher temperature than that of the younger illite however if illite coincidently precipitated with quartz which is supported by petrographic observation then illite with ages of about 200 ma in the eastern to central rotliegende sandstones of the area formed at a lower temperature but in more saline fluids than that of about 155 ma alternatively illite crystallization temperature and salinity of the interacting fluids could have been activated by the same hydrothermal activity at different locations in the studied area and could have decreased and changed respectively when the fluids moved in the sandstone reservoirs the potassium argon data fit a regional model of recurrent thermal activity with the oldest occurrence of authigenic illite in the eastern imbrock ganderkesee area and a time dependent trend of the hydrothermal activity toward the west previous results from northern germany central netherlands and the southern north sea complete the model with an initial activity at the same 200 ma time in the western offshore and central netherlands and an activity trend toward the east

tertiary tectonics and sedimentation in the salin fore arc basin myanmar salin basin of central myanmar is a tertiary fore arc basin that extends over 10 000 mi sup 2 and contains 30 000 ft of siliciclastic rocks in the western salin basin tertiary deltaic and fluvial formations contain thousands of feet of lithic sandstones that alternate with transgressive shallow marine shales facies and paleocurrent studies indicate deposition by north to south prograding tidal deltas and associated fluvial systems in a semi restricted basin presence of serpentinite and volcanic clasts in tertiary sandstones may imply that the basin was bounded to the east by the volcanic arc and to the west by a fore arc accretionary ridge throughout much of the cenozoic salin basin is currently defined by a regional north south trending syncline with uplifts along the eastern and western margins elongate folds along the eastern basin margin verge to the east and lie above the reverse faults that dip west much of myanmar s present hydrocarbon production is from these structures analogous structures occur along the western margin but verge to the west and are associated with numerous hydrocarbon seeps and hand dug wells these basin bounding structures are the result of fault propagation folding in the western salin basin major detachments occur within the shaly tabyin and laungshe formations fault ramps propagatedmore through steep forelimbs on the western sides of the folds resulting in highly asymmetric footwall synclines stratigraphic and apatite fission track data are consistent with dominantly plio pleistocene uplift with limited uplift beginning approximately 10 ma paleostress analysis of fault slickenside data indicates that fold and thrust structures formed during regional east west compression and are not related in any simple way to regional transpression as suggested by plate kinematics less

coseismic slip distributions of the 26 december 2004 sumatra andaman and 28 march 2005 nias earthquakes from gps static offsets static offsets produced by the 26 december 2004 m 9 sumatra andaman earthquake as measured by global positioning system gps reveal a large amount of slip along the entire 1300 km long rupture most seismic slip inversions place little slip on the andaman segment whereas both near field and far field gps offsets demand large slip on the andaman segment we compile available datasets of the static offset to render a more detailed picture of the static slip distribution we construct geodetic offsets such that postearthquake positions of continuous gps sites are reckoned to a time 1 day after the earthquake and campaign gps sites are similarly corrected for postseismic motions the newly revised slip distribution m w 9 22 reveals substantial segmentation of slip along the andaman islands with the southern quarter slipping 15 m in unison with the adjacent nicobar and northern sumatran segments of length 700 km we infer a small excess of geodetic moment relative to the seismic moment a similar compilation of gps offsets from the 28 march 2005 nias earthquake is well explained with dip slip averaging several meters mw 8 66 distributed primarily at depths greater than 20 km online material offset estimation procedure comparison of results to other stud ies and simpler solutions and tables of coseismic offsets

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

intraplate deformation of the indian subcontinent 1 while deformation at the earth s surface primarily occurs along tectonic plate boundaries major earthquakes have shaken regions deep within continental interiors three of the largest m 7 5 historic intraplate earthquakes occurred within the indian subcontinent suggesting the possibility of significant intraplate deformation we consider surface velocities determined from new gps data collected at 29 continuous gps stations and 41 survey mode gps stations in india between 1995 and 2007 to find a north south shortening rate of 0 3 0 05 nanostrain yr 1 which may be accommodated by 2 1 mm yr of more localized convergence across central india southward motions at 4 7 mm yr of sites on the shillong plateau in northeast india reflect rapid shortening and high earthquake hazard associated with active thrust faults bounding the plateau the width and magnitude of the elastic strain accumulation field across the himalaya varies little from 76 90 longitude but the strain is more broadly distributed and convergence rates are higher along the eastern 200 km of the range

fault creep and microseismicity on the hayward fault california implications for asperity size 1 the hayward fault is documented to undergo significant creep with some patches accommodating 50 or more of the long term fault displacement in spite of this the fault has also experienced moderate to large earthquakes by comparing the patterns of microseismicity observed on the fault with models of fault zone creep we can investigate the long term displacement deformation history of the fault in terms of the relative roles of aseismic creep fault slip accommodated through microseismicity and strain accumulation slip deficit we find that microseismicity on the hayward fault produces a negligible percentage of the seismic moment dissipated on the fault combining seismicity with our fault creep models allows us to calculate the size of asperities on the creeping fault for small asperities associated with repeating earthquakes on the hayward fault the rupture areas of these asperities range from 20 to 60 m2

postdepositional evolution of platform claystones based on a simulation of thermally induced diffusion of radiogenic 40ar from diagenetic illite abstract the lower cambrian lontova claystones contain well crystallized authigenic 1m illite mixed with detrital 2m illite part of the authigenic illite probably precipitated during sedimentation and subsequently experienced a temperature up to 140 c despite a limited burial to 500 1000 m the difference between the rb sr and k ar dates of this authigenic illite are attributed to preferential loss of radiogenic 40ar induced by a short lasting thermal pulse this interpretation is based on an ar diffusion model suggesting that the lontova blue clays were heated to around 140 c for 2 5 myr this thermal pulse could have occurred in relation with hot fluid migration induced by either tectonic dislocations in the basement rocks during the late silurian early devonian or rifting conditions during the permian by comparing rb sr and k ar data evaluation of radiogenic 40 ar losses by small authigenic illite particles at low temperatures could be a powerful tool for reconstruction of evolutionary histories of sedimentary successions that were either shallowly buried or percolated by migrating fluids released during tectono thermal activities

late cenozoic to holocene deformation in southwestern sichuan and adjacent yunnan china and its role in formation of the southeastern part of the tibetan plateau from at least 2 4 ma to present crust in the southeastern part of the tibetan plateau west of the convex east xianshuihe xiaojiang fault system has deformed internally and rotated clockwise around the eastern himalayan syntaxis the northwest striking ganzi fault zone bounds the rotating crust on the north and has a total left slip of 78 100 km of which 60 km is transferred to the xianshuihe fault zone across a diffuse transfer zone and 22 40 km is absorbed by bending of older structures and crustal shortening crustal shortening is expressed along and east of the eastern end of the ganzi fault zone by mountains capped by permanent glaciers locally rising nearly 1000 m above the average elevation of the tibetan plateau a similar transfer of left slip into shortening occurs farther south across the xianshuihe fault in the high mountains around and east of gongga shan 7556 m the northwest striking convex east left lateral litang fault zone lies southwest of the ganzi xianshuihe xiaojiang fault zone and appears to be less well developed but otherwise similar to the ganzi fault zone the batang chenzhi and other northeast striking right lateral faults of small displacement occur within the rotating crustal fragment together with the left slip faults they accommodate east west shortening northeast of the eastern himalayan syntaxis south of this region of shortening the crust is extending to form grabens within the dali and southern xiaojiang fault systems and in the tengchong volcanic province the progressive change from shortening southward into extension is related to variations in strain that characterize the region from northeast to southeast of the eastern himalayan syntaxis the assemblage of structures in southwestern sichuan geometrically resembles structures of eocene to miocene age in southern yunnan that were positioned northeast of the eastern himalayan syntaxis similar to present day southwestern sichuan at the time of their development the similarity in the structural development in the two areas indicates that crust northeast of the syntaxis underwent a common evolution as the syntaxis migrated northward during the past 50 m y structures in sichuan are less fully developed than older structures in southwestern yunnan and can serve as a guide to reconstruct the progressive tectonic development in the region of the syntaxis deformation in these areas indicates that plateau formation has been complex inhomogeneous and diachronous at scales from 1000 km to less than 100 km

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