comment on no late quaternary strike slip motion along the northern karakoram fault published by robinson et al in epsl 2015 abstract the northern part of the already highly debated karakorum fault kf in western tibet regarding its initiation age total geological offset and slip rate has been argued by robinson 2009a and robinson et al 2015 to be inactive this is based on field investigation and satellite images interpretation showing a few km of quaternary deposits from the southern tashkorgan basin in the chinese pamir that appear undisturbed by the main branch of the kf in particular robinson et al 2015 suggested that the kongur shan extensional system kes is not kinematically related to the kf and that the latter is only a local fault here we use basic definitions of what is an active strike slip fault system as well as re emphasize the importance of the timescale of observation to discuss whether a fault is active to demonstrate that the kf and the kes are part of the same fault system we argue that they together play a significant role in accommodating deformation at the western himalayan syntaxis under the form of extensional displacement in the chinese pamir

quaternary glaciation of the tashkurgan valley southeast pamir the quaternary glacial history of tashkurgan valley in the transition between the pamir and karakoram in xinjiang province china was examined using remote sensing field mapping geomorphic analysis of landforms and sediments and 10be terrestrial cosmogenic nuclide dating moraines were assigned to four glacial stages 1 the dabudaer glacial stage that dates to the penultimate glacial cycle and or earlier and may represent one or more glaciations 2 the tashkurgan glacial stage that dates to early last glacial most likely marine oxygen isotope stage mis 4 3 the hangdi glacial stage that dates to mis 2 possibly early mis 2 and 4 the kuzigun glacial stage that dates to the mis 2 possibly the global last glacial maximum and is younger than the hangdi glacial stage younger moraines and rock glaciers are present at the heads of tributary valleys but these were inaccessible because they are located close to politically sensitive borders with pakistan afghanistan and tajikistan glaciers during the dabudaer glacial stage advanced into the central part of the tashkurgan valley during the tashkurgan glacial stages glaciers advanced several kilometers beyond the mouths of the tributary valleys into the tashkurgan valley glaciers during the hangdi and kuzigun glacial stages advanced just beyond the mouths of the tributary valleys glaciation in this part of the himalayan tibetan orogen is likely strongly controlled by northern hemisphere climate oscillations although a monsoonal influence on glaciation cannot be ruled out entirely

a doubling of the post perovskite phase boundary and structure of the earth s lowermost mantle a new model of the deep earth allows geophysicists to measure variations in earth s temperature near the boundary between the rocky mantle and core using a recently discovered phase change in the lowest part of the earth s mantle where atoms rearrange themselves in crystals under extreme pressure and temperature the model also explains odd features of this part of the mantle such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting combined with observations the results imply very large variations in temperature providing further evidence for circulation of material throughout the earth s mantle the thermal structure of the earth s lowermost mantle the d layer spanning depths of 2 600 2 900 kilometres1 is key to understanding the dynamical state and history of our planet earth s temperature profile the geotherm is mostly constrained by phase transitions such as freezing at the inner core boundary or changes in crystal structure within the solid mantle that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory a recently discovered phase transition at pressures of the d layer2 3 4 is ideally situated to reveal the thermal structure of the lowermost mantle where no phase transitions were previously known to exist here we show that a pair of seismic discontinuities observed in some regions of d can be explained by the same phase transition as the result of a double crossing of the phase boundary by the geotherm at two different depths this simple model can also explain why a seismic discontinuity is not observed in some other regions and provides new constraints for the magnitude of temperature variations within d

no late quaternary strike slip motion along the northern karakoram fault abstract models that treat long term evolution of the tibetan orogen in terms of interactions between rigid blocks require the right slip karakoram fault that bounds the western margin of the tibetan plateau to be a long lived stable high slip rate feature while the southern portion of the fault clearly remains active recent work has proposed that the northern half of the karakoram fault is currently inactive new field observations and geochronologic results from the northern end of the karakoram fault system confirm this interpretation and provide the first quantitative data on the minimum age for the termination of slip in the southeast pamir gravel that yields a u series age of 198 5 ka on secondary carbonate caps a non deformed strath terrace that extends across the main strand of the karakoram fault the secondary achiehkopai fault strand is overlain by undisturbed hangdi glacial stage 24 6 ka deposits and dabudar glacial stage penultimate glacial cycle 150 ka or older deposits which lack observable lateral displacement or deformation together these observations show that the northern portion of the karakoram fault system has not accommodated any detectable strike slip deformation since at least 24 6 ka and most likely since 200 ka or more these results show that the karakoram fault system no longer forms a continuous discrete kinematic boundary at the western margin of the tibetan plateau this suggests that even long 500 km strike slip faults within orogenic belts are inherently unstable features consistent with models of continental collision zones involving relatively weak crust and distributed deformation

kinematics of the pamir and hindu kush regions from gps geodesy 1 gps velocities measured in the pamir and surrounding regions show a total of 30 mm yr of northward relative motion between stable pakistan and eurasia the convergence budget is partitioned into 10 15 mm yr of localized shortening across the trans alai thrust which bounds the pamir on the north consistent with southward subduction of intact lithosphere another 10 15 mm yr of shortening is distributed across the chitral himalaya and hindu kush suggesting that hindu kush seismicity might be related to northward subduction of indian lithosphere modest shortening at 5 mm yr occurs north of the trans alai thrust across the south tien shan and between the ferghana valley and eurasia negligible north south shortening occurs within the high pamir but as much as 5 mm yr and perhaps 10 mm yr of east west extension occurs within this region this extension is matched by a comparable amount of east west shortening in the tajik depression the localization of shortening to the margins of the pamir combined with observations of distributed internal extension implies that the east west vertically averaged horizontal compressive normal stress is smaller than the north south compressive stress

tectonic evolution of the northeastern pamir constraints from the northern portion of the cenozoic kongur shan extensional system western china the late cenozoic kongur shan extensional system lies along the northeastern margin of the pamir at the western end of the himalayan tibetan orogen accommodating east west extension in the pamir at the northern end of the extensional system the kongur shan normal fault juxtaposes medium to high grade metamorphic rocks in both its hanging wall and footwall which record several mesozoic to cenozoic tectonic events schists within the hanging wall preserve a buchan metamorphic sequence dated as late triassic to early jurassic 230 200 ma from monazite inclusions in garnet metamorphic ages overlap with u pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the paleo tethys ocean the northern portion of the footwall of the extensional system exposes an upper amphibolite facies unit 650 c 8 kbar which structurally overlies a lowgrade metagraywacke unit the high grade unit records late early cretaceous crustal thickening at ca 125 110 ma followed by emplacement over the low grade metagraywacke along a north northeast directed thrust prior to ca 100 ma together these results indicate signifi cant middle cretaceous crustal thickening and shortening in the northern pamir prior to the indo asian collision a third late miocene ca 9 ma amphibolite facies metamorphic event 650 700 c 8 kbar is recorded in footwall gneisses of the kongur shan massif north of the kongur shan massif rapid cooling in the footwall beginning at 7 8 ma is interpreted to date the initiation of exhumation along the kongur shan normal fault a minimum of 34 km of east west extension is inferred along the kongur shan massif based on the magnitude of exhumation since the late miocene 29 km and the present dip of the kongur shan normal fault 40 field observations and interpretation of satellite images along the southernmost segment of the kongur shan extensional system indicate that the magnitude of late cenozoic east west extension decreases signifi cantly toward the south this observation is inconsistent with models in which east west extension in the pamir is driven by northward propagation of the right slip karakoram fault suggesting instead that extension is driven by vertical extrusion due to topographic collapse radial thrusting along the main pamir thrust or oroclinal bending of the entire pamir region

paleointensities from a cretaceous basalt platform in inner mongolia northeastern china abstract thellier s paleointensity experiments were carried out using cretaceous basalts of 90 ma which were taken from a basalt platform in inner mongolia northeastern china hysteresis parameters indicate that bulk grain size is psd in all samples js t curves indicate that the main magnetic mineral is titanomagnetite with curie temperature tc of 200 350 c with minor phases of higher tc which is known from the long tails continuing to the tc of magnetite samples often undergo severe chemical alteration on heating resulting in a decrease of trm capacity over the temperature range of 300 350 c nevertheless successful results were obtained from 47 of the total of 30 samples for the temperature steps lower than this critical point combining two results from possible identical flows four paleointensities were obtained ranging from 10 to 36 t which corresponds to a virtual dipole moment vdm of 1 8 6 0 1022 am2 these results support a low dipole moment during the later period of the cretaceous long normal superchron lns

cenozoic episodic uplift and kinematic evolution between the pamir and southwestern tien shan abstract the pamir salient and southwestern tien shan belong to two different systems which collided due to the continuous northward drift of the indian plate during the cenozoic resulting in a shortening of 300 km the uplift history and kinematic evolution of the pamir southwestern tien shan remain unclear in this study we chose the 2025 m thick pakabulake formation in the east wuqia section at the southern most margin of the southwestern tien shan system to obtain a high resolution magnetostratigraphic record spanning 16 61 ma to 9 78 ma based on its high sedimentation rate stable ca e w paleocurrents and stable magnetic susceptibility values the nearby southwestern tien shan was inferred to have undergone stable uplift during this period of sedimentation combining our results with the previous low temperature thermochronology magnetostratigraphy and re calculated block rotations we conclude that four episodic uplift events occurred in the pamir southwestern tien shan during the cenozoic at times of 50 40 ma 35 16 ma 11 7 ma and

high geomagnetic intensity during the mid cretaceous from thellier analyses of single plagioclase crystals recent numerical simulations have yielded the most efficient geodynamo having the largest dipole intensity when reversal frequency is low reliable paleointensity data are limited but heretofore have suggested that reversal frequency and paleointensity are decoupled we report data from 56 thellier thellier experiments on plagioclase crystals separated from basalts of the rajmahal traps 113 to 116 million years old of india that formed during the cretaceous normal polarity superchron these data suggest a time averaged paleomagnetic dipole moment of 12 5 1 4 1022 amperes per square meter three times greater than mean cenozoic and early cretaceous late jurassic dipole moments when geomagnetic reversals were frequent this result supports a correlation between intervals of low reversal frequency and high geomagnetic field strength

the cretaceous superchron geodynamo observations near the tangent cylinder abstract if relationships exist between the frequency of geomagnetic reversals and the morphology secular variation and intensity of earth s magnetic field they should be best expressed during superchrons intervals tens of millions of years long lacking reversals here we report paleomagnetic and paleointensity data from lavas of the cretaceous normal polarity superchron that formed at high latitudes near the tangent cylinder that surrounds the solid inner core the time averaged field recorded by these lavas is remarkably strong and stable when combined with global results available from lower latitudes these data define a time averaged field that is overwhelmingly dominated by the axial dipole octupole components are insignificant these observations suggest that the basic features of the geomagnetic field are intrinsically related superchrons may reflect times when the nature of core mantle boundary heat flux allows the geodynamo to operate at peak efficiency

quantification of both normal and right lateral late quaternary activity along the kongur shan extensional system chinese pamir the kongur shan extensional system kes is a 250 km long normal fault system that bounds the muji tashkorgan basin of the chinese pamir it accommodates e w extension due to the northward indentation of the pamir salient and its late miocene activity has been the focus of tectonic studies while the kes has a main normal component wnw ese striking segments have an additional right lateral strike slip component here we quantify late quaternary horizontal and vertical slip rates at three locations along the kes where active faults cut and offset abandoned geomorphic features we find rates of 3 4 mm a 1 horizontal along the western muji fault in the north and of 1 7 mm a 1 vertical and 1 mm a 1 horizontal along the kongur shan fault in the south during the late pleistocene these rates are consistent with gps and late miocene rates and imply that e w extension in the muji tashkorgan basin is faster in the north than in the south

palaeointensities determined from the middle cretaceous basalt in liaoning province northeastern china abstract a palaeomagnetic and geochronologic investigation has been conducted on a basalt lava sequence at jianguo in liaoning province northeastern china radiometric 40 ar 39 ar dating experiments indicate the volcanism occurred in relatively short time intervals between 105 5 and 102 2 ma thermomagnetic experiments and electron microprobe show that main primary carrier of remanence to be titanomagnetite with curie temperature of 300 c a modified version of the thellier thellier technique with systematic partial thermoremanent magnetization ptrm checks was used for palaeointensity determinations fourteen out of 61 samples from the studied lavas yield reliable palaeointensity estimates with a mean virtual dipole moment vdm of 4 07 0 2 1022 am2 about half the strength of the modern day field

new palaeointensity results from cretaceous basalt of inner mongolia china we present new thellier thellier palaeointensity results from three cooling units 32 samples of inner mongolia lava flows 91 7 ma emplaced during the cretaceous normal superchron cns based on rock magnetic and microscopy observations the magneto mineralogy of all samples is determined to be primary and unaltered high ti titanomagnetite accepted palaeointensity determinations obtained in the 80 200 c temperature interval are of good technical quality with positive standard partial thermoremanent magnetisation ptrm checks and ptrm tail checks obtained palaeointensity estimates range from 14 7 to 28 0t with virtual axial dipole moments vadm of 2 4 to 4 6 10 22 am 2 the data agree well with recently published results from the same region and combining the two datasets we obtain independent estimates from six different cooling units yielding a time averaged vadm of 3 2 1 6 10 22 am 2 these data suggest a relatively low dipole moment towards the end of the cretaceous normal superchron

evidence for weak geomagnetic field intensity prior to the cretaceous normal superchron abstract a palaeomagnetic and geochronologic investigation has been carried out on a sequence of 19 lava flows at sihetun in northeastern china age determinations by k ar dating indicate that the sequence spans 124 133 ma that is the time just prior to cretaceous normal superchron cns rock magnetic measurements of thermomagnetic curves and hysteresis loops show the primary carrier of remanence to be pseudo single domain magnetite stepwise thermal demagnetization successfully isolated a well defined direction of characteristic magnetization chrm in all the lavas the mean palaeodirection determined is d i 5 4 58 7 95 2 4 and d i 175 9 60 0 95 6 4 for 15 normally magnetized flows and 3 reversely magnetized flows respectively one lava was found to possess an intermediate direction of magnetization the inferred palaeolatitude of the sampling site is very similar to the present day position supporting the contention that suturing between the mongolia and north china plates was probably completed by the late jurassic and that subsequently little rotation or translation occurred in the region west of the tanlu fault zone thellier thellier palaeointensity experiments with systematic partial thermoremanent magnetization ptrm checks were conducted on 66 samples from 13 lava flows results from the 29 samples 44 which met strict reliability criteria indicate a range of virtual dipole moments vdms from 2 83 to 4 17 1022 a m2 with an average of 3 53 0 02 1022 a m2 this finding helps confirm that a weak geomagnetic field probably occurred just prior to the cns

fault geometry of 2015 mw7 2 murghab tajikistan earthquake controls rupture propagation insights from insar and seismological data abstract combining space based geodetic and array seismology observations can provide detailed information about earthquake ruptures in remote regions here we use landsat 8 imagery and alos 2 and sentinel 1 radar interferometry data combined with data from the european seismology network to describe the source of the december 7 2015 mw7 2 murghab tajikistan earthquake the earthquake reactivated a 79 km long section of the sarez karakul fault a ne oriented sinistral trans tensional fault in northern pamir pixel offset data delineate the geometry of the surface break and line of sight ground shifts from two descending and three ascending interferograms constrain the fault dip and slip solution two right stepping ne striking segments connected by a more easterly oriented segment sub vertical or steeply dipping to the west were involved the solution shows two main patches of slip with up to 3 5 m of left lateral slip on the southern and central fault segments the northern segment has a left lateral and normal oblique slip of up to a meter back projection of high frequency seismic waves recorded by the european network processed using the multitaper music approach focuses sharply along the surface break the time progression of the high frequency radiators shows that after a 10 second initiation phase at slow speed the rupture progresses in 2 phases at super shear velocity 4 3 5 km s separated by a 3 second interval of slower propagation corresponding to the passage through the restraining bend the intensity of the high frequency radiation reaches maxima during the initial and middle phases of slow propagation and is reduced by 50 during the super shear phases of the propagation these findings are consistent with studies of other strike slip earthquakes in continental domain showing the importance of fault geometric complexities in controlling the speed of fault propagation and related spatiotemporal pattern of the high frequency radiation

spatially constant slip rate along the southern segment of the karakorum fault since 200 ka abstract determining the slip rate history along the right lateral karakorum fault kf is fundamental to understanding its present day kinematic role in the deformation of tibet geodetic and geologic studies suggest slip rates of 0 11 mm yr along this structure whether slip rate variability exists along strike and or time or simply results from different measuring techniques timescales remains unknown in order to constrain slip rates within a timescale of 200 ka we studied fluvial and glacial geomorphic features that are right laterally or vertically offset by the fault by varying amounts from 7 1 m to 430 30 m and up to 53 5 m respectively we constrained their ages using 10be surface exposure dating on 141 quartz rich samples collected on 4 lateral moraines and at 3 alluvial sites along the southernmost segment of the kf menshi kailas basin and along the gurla mandhata detachment fault in the pulan graben from the 30 fault bend at baer 80 5 e to mount kailas area the slip rate along the kf is 7 1 3 2 1 7 mm yr at menshi and 7 9 3 2 2 5 mm yr at kailas slip on two parallel fault strands in the pulan graben the normal fault slip rate is 1 6 0 4 0 3 mm yr our data suggest that the quaternary slip rate along the southern kf does not decrease eastward but is constant along strike for at least 200 km from 5 11 mm yr in the gar basin further north to 7 8 mm yr in the menshi kailas basin because no expected along strike slip rate gradient is observed it implies that the kf does not end at the kailas but must extend where the slip rate decreases i e eastward along the yarlung zangbo suture and southward along the gurla mandhata humla fault system

limit of strain partitioning in the himalaya marked by large earthquakes in western nepal great earthquakes in the himalaya are thought to occur mostly along the range front field mapping and radiocarbon dating reveal earthquake rupture on a previously unrecognized fault in the interior of the western himalaya which forms part of a key structural component of the mountain range implying that seismic risk evaluations should be revised

geomagnetic palaeointensity just prior to the cretaceous normal superchron abstract a combined geochronologic k ar and palaeomagnetic study has been conducted on a basalt lava sequence at zhuanchengzi in liaoning province northeastern china the new k ar age obtained from these lava flows is 120 93 0 88 ma marine anomaly m0 detailed investigations were conducted on two samples from each lava flow to determine their rock magnetic properties the temperature dependences of the saturation magnetization j t and the initial susceptibility t show evidence of low titanium magnetite and a curie temperature of 560 585 c with generally good reversibility of heating and cooling curves hysteretic properties ratios of mrs ms and hcr hc indicate that pseudo single domain psd grains of magnetite are dominant in these lavas stepwise thermal demagnetization isolated well defined characteristic magnetization chrm in all the 20 lava flows with a mean direction of d i 174 9 60 1 with 95 2 3 the modified version of the thellier and thellier palaeointensity method coe 1967a with systematic partial thermoremanent magnetization ptrm checks was used forty two of 71 samples 59 yielded reliable palaeointensity results virtual dipole moment vdm values range from 1 71 1022 to 5 27 1022 a m2 with an average of 3 96 0 07 1022 a m2 this low dipole field intensity value is approximately half the present day vdm consistent with older results obtained from the caribbean submarine basalt glasses for the period of 125 1 ma pick and tauxe 1993 this suggested that a weak geomagnetic field probably occurred just prior to the cretaceous normal superchron cns

geologic offsets across the northern karakorum fault implications for its role and terrane correlations in the western himalayan tibetan orogen abstract while the 1000 km long karakorum right slip fault is one of the most prominent structures in the himalayan tibetan orogen considerable disagreement exists as to the total magnitude of offset across the fault and the role it has played in accommodating convergence between india and asia using satellite images i have correlated a well defined carbonate unit the late triassic early jurassic aghil formation across the northern portion of the karakorum fault from the southwest pamir to the tianshuihai terrane of western tibet the northern and southern exposure limits of the aghil formation have 149 167 km of separation which i interpret to represent the magnitude of displacement on the northern karakorum fault these values overlap with estimates correlating the bangong nujiang and shyok sutures across the central karakorum fault and maximum offsets of the miocene baltoro granite and rule out correlations of the bangong nujiang suture and the rushan pshart suture the displacement yields a geologic slip rate of 10 8 1 3 mm yr using an initiation age of 14 7 1 ma or 6 89 0 8 mm yr with an initiation age of 23 1 ma this result supports previous work showing limited offset across the karakorum fault and indicates that the fault that has not accommodated either large magnitudes i e 100 s of km of eastward lateral extrusion of tibet or hundreds of kilometers of offset between terranes of the western and central portions of the orogenic belt

contemporary crustal deformation within the pamir plateau constrained by geodetic observations and focal mechanism solutions we used an updated data set of 192 gps derived surface velocities and 393 earthquake focal mechanisms mw 3 0 hypocenter depths 30 km to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the pamir plateau and its surrounding regions the strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regional scale stress inversion drssi method of hardebeck and michael journal of geophysical research https doi org 10 1029 2005jb004144 2006 the results show that the crustal stress field around the pamir plateau is predominantly characterized by nnw sse compression and e w extension which is consistent with the principal orientations of the two dimensional surface strain rate tensor this agreement supports the notion that the pamir and southwestern tien shan are uniformly strained blocks in particular the fan shaped rotational pattern between text shmax and the strain rate from the western pamir to the tajik basin shows that the counterclockwise rotation of the text shmax orientation is associated with vertical deformation which is consistent with the idea of schurr et al tectonics 33 8 2014tc003576 2014 concerning the gravitational collapse and westward extrusion of the crust in the western pamir we propose that such a stress strain pattern dominated by nnw ese oriented compression and e w trending extension originated from a combination of the northward push of the indian continent and the southward subduction of the tien shan

response of earth s magnetic field to large lower mantle heterogeneity abstract a simplified two fold pattern of convection in the earth s core is often used to explain the non axisymmetric magnetic flux concentrations in the present day geomagnetic field for large lateral variations in the lower mantle heat flux however a substantial east west dichotomy in core convection may be expected this study examines the effect of a large lateral variation in heat flux at the outer boundary in cylindrical annulus experiments that achieve approximate geostrophy of the convection as well as in rapidly rotating spherical shell simulations in either geometry the imposed boundary heat flux is derived from the seismic shear wave velocity in the lowermost mantle the pattern of large scale convection in the simulations closely follows that in the annulus experiments which suggests that the lateral buoyancy at the equator essentially determines the structure of core convection in particular the location of a coherent downwelling that forms beneath canada in mildly driven convection entirely switches over to the siberian region in strongly driven states spherical dynamo models in turn show that this eastward migration of convection causes the relative instability or even the disappearance of the high latitude magnetic flux in the western hemisphere finally large radial buoyancy causes homogenization of convection which may place an upper bound for the rayleigh number in the core

distributed deformation in southern and western tibet during and after the india asia collision field and radiometric data are used to describe and date strain and stress states in southern longitude 88 o to 91oe latitude 28 o to 30on and western tibet longitude 79 o to 82oe latitude 30 o to 34on we factorize deformation into syncollisional and postcollisional and we present stretching lineation and displacement orientation maps two sections across the indian shelf sequence and stress orientations calculated from mesoscale fault slip data in southern tibet syncollisional stretching and displacement directions trend 90 46 o and displacement is top to south synkinematic low grade metamorphism is dated at 50 ma at one locality in the indian shelf sequence underlying the main mantle thrust of the indus yarlung suture this implies paleocene onset of continental collision for the investigated section postcollisional structures comprise a backthrust group which includes foreland and hinterland directed thrusts reverse and strike slip faults and folds it dominates postcollisional deformation is concentrated along the indus yarlung suture and portrays n s compression otrend of 8o 17 o o2 of 97o 17o a strike slip group consists of conjugate strike slip faults is concentrated in east trending narrow highly deformed zones and indicates that n s compression is locally compensated by e w extension oof 15o 29 o o3 of 103o 30o synkinematic muscovite dates postcollisional deformation as late early miocene 17 5 ma at one locality at the suture strike slip and oblique normal 03 of 600 23 o oof 144o 21 o and normal o3 114o 16 o faulting dated between late miocene and recent and including active deformation represents dominant e w and minor n s extension due to e w stretching of southern tibet and oroclinal bending along the himalayan arc restoring syncollisional and postcollisional deformation yields a minimum of 67 258 km shortening across the indian shelf sequence incorporating recently published contraction estimates across the eastern himalaya yields minimum shortening between undeformed india and the indus yarlung suture of 66 536 km the himalaya tibet orogenic system south of the indus yarlung suture had an initial width of 811 km in the southern tibetan section in western tibet imbrication of an ophiolite sequence of the bangong nujiang suture is top to south stretching lineation trend of 15o 18o and o3 of active deformation trends ese faulting along the shiquanhe fault zone which transfers displacement from the northern part of the karakorum fault to a system of rifts in western central tibet indicates dextral strike slip alternating with sinistral oblique normal faulting and block rotations around vertical axes during a prolonged shearing history the indian shelf sequence south of mount kailas shows top to south imbrication stretching lineation trend of 52o 60o both indian shelf rocks and oligocene miocene kailas conglo merates record backthrusting and backfolding oof 33 o and recent e w extension 03 of 85o 28o

evidence against quaternary slip on the northern karakorum fault suggests kinematic reorganization at the western end of the himalayan tibetan orogen abstract while the right slip karakorum fault is one of the most prominent structures in the himalayan tibetan orogen its evolution and role in accommodating deformation related to the collision between india and asia is controversial different models interpret the karakorum fault as either 1 a long lived stable feature analogous to a plate boundary structure or 2 an evolving fault system with limited displacement 150 ka overly the trace of the two strands of the karakorum fault and show no evidence of tectonic disturbance 2 older late pliocene to early quaternary loess deposits which overlie the trace of the fault are either undisturbed or are cut by small normal fault scarps with no evidence of strike slip displacement 3 east west trending bedrock incised stream valleys up to 500 m deep cross both strands of the fault with no sign of lateral deflection i suggest that termination of slip along the northern segment of the karakorum fault occurred in the pliocene due to southward propagation of the altyn tagh fault system along the longmu co gozha co fault and impingement of the karakorum fault this study suggests that large intracontinental strike slip faults embedded within orogenic plateaus are transient features which should be expected to have complicated kinematic histories and short life spans relative to the life of an orogenic belt

correlation of earth s magnetic field with lower mantle thermal and seismic structure abstract variations in the earth s lower mantle appear to influence the geodynamo operating in the liquid core we present a solution to the full dynamo equations with lateral variations in heat flux on the outer boundary defined by the shear wave velocity of the lowermost mantle the magnetic field is almost stationary and locked to the boundary with 4 symmetrical concentrations of flux sited beneath cold mantle this allows for the first time a direct comparison between a dynamo solution and the main features of the present geomagnetic field of the four main equatorially symmetric flux lobes two the siberian pair are centered within 5 of the corresponding earth s pair the other two the canadian pair are not quite so close but are more mobile as the corresponding earth s pair have been in the last 300 years our study strongly suggests that geomagnetic field morphology is dominated not only by geometry related to the inner core but also by structure in the bottom few hundred kilometres of the mantle notably the seismically fast ring beneath the pacific rim and large fast anomalies beneath siberia and canada tighter locking of one of the pairs of flux lobes suggests the seismic anomaly beneath the siberian side of the ring is in some way stronger than the one on the canadian side these locked solutions only occur for a limited parameter range with the large ekman numbers available to numerical experiments which explains why none have been found earlier this solution provides an important starting point for further searches for dynamos with realistic geomagnetic fields

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

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

late quaternary slip rate along the central bangong chaxikang segment of the karakorum fault western tibet insight into the spatial and temporal changes of slip rate is essential to understand the kinematic role of large strike slip faults in continental collision zones geodetic and geologic rates from present to several million years ago along the karakorum fault range from 0 to 11 mm yr here we determine the first late quaternary slip rate at the southern end of the linear bangong chaxikang segment of the karakorum fault using cumulative offsets 20 200 m of fans and terraces at three sites as well as 74 new 10 be surface exposure ages to constrain the age of these offset geomorphic markers the rate is 3 mm yr at sites gun and chaxikang and it is 1 7 2 2 mm yr at the gar fan site together with rates obtained along the southernmost menshi kailas segment the karakorum fault slip rate seems to increase southeastward from south of bangong lake to kailas from 3 to 8 mm yr these karakorum fault slip rate data 3 8 mm yr together with the total length of the fault 1000 km and its initiation age 13 23 ma confirm that the karakorum fault is the major fault accommodating dextral strike slip motion ne of the western himalayas the dextral karakorum fault in the south and the conjugate left lateral longmu co altyn tagh fault system in the north are thus the major strike slip faults of western tibet which contribute to eastward extrusion of tibet

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

cumulative and coseismic during the 2016 m w 6 6 aketao earthquake deformation of the dextral slip muji fault northeastern pamir orogen

time independent and time dependent behaviour of high latitude flux bundles at the core mantle boundary 1 using a numerical dynamo model we examine whether quasi stationary high latitude flux bundles which are observed in the geomagnetic field over the last 300 years and possibly over much longer time periods result from thermal core mantle interactions we do so by imposing lateral heat flux variations at the core mantle boundary based upon the dominant pattern of seismic heterogeneity in the lowermost mantle we find that the time averaged field then has a similar arrangement of flux bundles to that observed during the last few hundred years however the field is time dependent and this arrangement of flux bundles is not a feature of the field at all times

first tectonic geomorphology study along the longmu gozha co fault system western tibet abstract the longmu gozha co left lateral strike slip fault system lgcf is located in remote western tibet forming a triple junction with both the altyn tagh fault atf and the karakorum fault kf the two major strike slip faults in the region the ashikule gozha co and longmu co faults are clear and distinct left stepping en echelon faults together forming the lgcf system although poorly documented quantifying its activity remains a key problem to understand the kinematics and the tectonic history of the westernmost tibetan plateau indeed the karakax fault nw segment of the atf lgcf and kf together control the tectonics of western tibet which itself controls the extrusion of tibet towards the east with the lgcf acting as a natural boundary for eastward motion of the tibetan plateau due to india s northward impingement the lgcf system shows clear and impressive morphological indications of left lateral active shear that we quantify using field measurements terrestrial lidar along with 10 be surface exposure dating our data suggest a slip rate 9 and 8 mm yr respectively yielding a few mm yr of extension accommodated most likely in the ashikule graben and surroundings located between the atf and karakax faults numerous evidences of recent tectonic related events are present in the vicinity such as the 1951 volcanic eruption as well as the 2008 and 2014 ms 7 3 yutian earthquakes attesting of its high activity in addition the lgcf s en echelon geometry and identical direction with the atf as well as smaller geological offsets and lower slip rate compared to those on the surrounding faults suggest that this segment of the atf may be the most recent

cretaceous geomagnetic paleointensities thellier experiments on pillow lavas and submarine basaltic glass from the ontong java plateau 1 we present new thellier paleointensity results on pillow lavas and pillow rim submarine basaltic glass sbg from 120 ma basalts erupted on the ontong java plateau all pillow lavas have suffered low temperature alteration and are unsuitable for thellier paleointensity experiments in contrast pillow rim sbg is virtually impermeable to seawater and therefore has suffered little or no low temperature alteration out of 21 selected sbg samples with magnetic moment larger than 10 10 am2 18 samples from 12 chilled sbg margins yielded paleointensity estimates of good technical quality rock magnetic measurements show the primary carrier of remanence is low ti titanomagnetite occurring in a continuous range of compositions starting from nearly pure magnetite as suggested by a recent study magnetic hysteresis parameters were monitored during the entire paleointensity experiment and a drastic change of parameters was observed above 400 440 c which is in accordance with the partial thermoremanent magnetization checks failing significantly above the same temperature we suggest that paleointensity estimates obtained below this critical temperature represent true determination of the paleomagnetic field strength for several pillow margins two to three samples were measured and in such cases the data agree well altogether we obtain reliable estimates from 12 sbg pillow rims yielding a mean paleointensity of 27 1 13 4 t and a corresponding virtual axial dipole moment of 5 8 2 8 1022 am2 this value is slightly higher than whole rock data from similar aged subaerial lava flows the paleosecular variation of the intensity estimates is slightly larger than previously reported for paleointensity determinations for the cretaceous normal superchron

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

effects of thermally heterogeneous structure in the lowermost mantle on the geomagnetic field strength abstract we have conducted a study of numerical dynamos in a rapidly rotating spherical shell with prescribed non uniform heat flux patterns at the outer boundary to examine effects of thermal structure at the core mantle boundary cmb on the geodynamo especially on the magnetic field strength large heat flux heterogeneity with equatorial symmetry enhances strength of the dipolar magnetic field for a sufficiently small ekman number whereas that with equatorial anti symmetry does not change the strength but affects the tilt of the magnetic dipole axis the thermal wind induced by heat flux heterogeneity at the cmb has strong influence on the flow structure and on the magnetic field intensity these results suggest that thermally heterogeneous structure of the lowermost mantle might give rise to an anomalously strong geomagnetic field such as that during the cretaceous normal superchron

fast slip rate along the northern end of the karakorum fault system western tibet 1 the exact location of the northern karakorum fault kf in western tibet is unclear and its current activity is debated here we investigate the possible northern extension of the kf the muji fault located in the chinese pamir which belongs to the kongur shan extensional system and provide the first quantitative estimate of its holocene slip rate the fault cuts and offsets a series of 6 fluvial terraces yielding a minimum slip rate of 4 5 0 2 mm yr by matching the largest terrace riser offset with its upper surface age 10be n 24 field evidences of right lateral movement along the kongur shan fault as well as geometry and kinematic similarities with the southern half of the kf attest that the muji fault belongs to the kf system therefore its fast slip rate combined with the slow slip rates along minor splays of the northern kf maybe up to 4 mm yr southwest of the tashkorgan basin agrees with the late pleistocene southern kf slip rate 8 mm yr

seismostratigraphy and thermal structure of earth s core mantle boundary region we used three dimensional inverse scattering of core reflected shear waves for large scale high resolution exploration of earth9s deep interior d and detected multiple piecewise continuous interfaces in the lowermost layer d beneath central and north america with thermodynamic properties of phase transitions in mantle silicates we interpret the images and estimate in situ temperatures a widespread wave speed increase at 150 to 300 kilometers above the coremantle boundary is consistent with a transition from perovskite to postperovskite internal d stratification may be due to multiple phase boundary crossings and a deep wave speed reduction may mark the base of a postperovskite lens about 2300 kilometers wide and 250 kilometers thick the core mantle boundary temperature is estimated at 3950 200 kelvin beneath central america a site of deep subduction the d is relatively cold t 700 100 kelvin accounting for a factor of two uncertainty in thermal conductivity core heat flux is 80 to 160 milliwatts per square meter mw m 2 into the coldest d region and 35 to 70 mw m 2 away from it combined with estimates from the central pacific this suggests a global average of 50 to 100 mw m 2 and a total heat loss of 7 5 to 15 terawatts

magnetic boundary layers in numerical dynamos with heterogeneous outer boundary heat flux abstract it has been proposed that magnetic flux expulsion due to outer core fluid upwellings may affect the geomagnetic secular variation on the core mantle boundary bloxham 1986 in this process intense horizontal field lines are concentrated below the outer boundary introducing small radial length scales and consequently strong radial diffusion here we explore such magnetic boundary layers in numerical dynamo simulations with heterogeneous outer boundary heat flux inferred from a tomographic model of lower mantle seismic shear waves velocity anomalies our scheme associates magnetic boundary layers to peak horizontal magnetic fields at the top of the shell in our models mean magnetic boundary layer thickness ranges 200 400 km and decreases with increasing magnetic reynolds number extrapolation or interpolation to earth s core conditions based on total core flow amplitude or its poloidal part gives mean magnetic boundary layer thickness of 220 and 260 330 km respectively we find magnetic boundary layers associated with the azimuthal field at the equatorial region whereas magnetic boundary layers associated with the meridional field are found at mid latitudes negative outer boundary heat flux anomalies yield preferred locations of expulsion of azimuthal field below africa and the pacific while positive outer boundary heat flux anomalies yield preferred locations of expulsion of meridional field below the americas and east asia furthermore we find a tendency of the azimuthal field to low latitudes of the northern hemisphere our results suggest that the local diffusion time is on the order of several kyr and the local magnetic reynolds number is on the order of 10 both much smaller than classical estimates

co seismic and cumulative offsets of the recent earthquakes along the karakax left lateral strike slip fault in western tibet abstract the 400 km long karakax left lateral strike slip fault is the westernmost segment of the altyn tagh fault it separates northwestern tibet to the south from the tarim basin to the north the western section of the karakax fault exhibits clear co seismic surface ruptures of past large earthquakes geomorphic offset measurements from the field and high resolution ikonos images along 1 5 km across the sanshiliyingfang fan and along 55 km of the fault range from 3 to 28 m with distinct clusters at 6 2 3 14 2 19 2 and 24 3 m the cluster of the smallest offsets around 6 m full range from 3 to 10 m distributed over a minimum length of 55 km is attributed to the last largest surface rupturing event that testifies of the occurrence of a magnitude mw 7 4 7 6 earthquake along the karakax fault we interpret the other offset clusters as the possible repetition of similarly sized events thus favoring a characteristic slip model for the karakax fault in a 3 m deep trench dug across the active trace of the fault we can identify the main rupture strands of the last and penultimate events the penultimate event horizon a silty sand layer has been radiocarbon dated at 975 1020 ad ams 14 c age it is proposed that large mw 7 4 7 6 events with co seismic slip of about 6 m rupture the karakax fault with a return time of about 900 years implying an average slip rate of about 6 7 mm years during the late holocene these results suggest that the karakax fault is the largest left lateral strike slip fault at the rim of northwestern tibet accommodating eastward movement of tibet due to the india eurasia collision

mantle driven geodynamo features effects of compositional and narrow d anomalies abstract lower mantle heterogeneity could cause deviations from axial symmetry in geodynamo properties global tomography models are commonly used to infer the pattern of core mantle boundary heat flux via a linear relation that corresponds to a purely thermal interpretation of lower mantle seismic anomalies ignoring both non thermal origins and non resolved small scales here we study the possible impact on the geodynamo of narrow thermal anomalies in the base of the mantle originating from either compositional heterogeneity or sharp margins of large scale features a heat flux boundary condition composed of a large scale pattern and narrow ridges separating the large scale positive and negative features is imposed on numerical dynamos we find that hot ridges located to the west of a positive large scale core mantle boundary heat flux anomaly produce a time average narrow elongated upwelling a flow barrier at the top of the core and intensified low latitudes magnetic flux patches when the ridge is located to the east of a positive core mantle boundary heat flux anomaly the associated upwelling is weaker and the homogeneous dynamo westward drift leaks precluding persistent intense low latitudes magnetic flux patches these signatures of the core mantle boundary heat flux ridge are evident in the north south component of the thermal wind balance based on the pattern of lower mantle seismic tomography masters et al 2000 we hypothesize that hot narrow thermal ridges below central asia and the indian ocean and below the american pacific coast produce time average fluid upwelling and a barrier for azimuthal flow at the top of the core east of these ridges below east asia and oceania and below the americas time average intense geomagnetic flux patches are expected

slabs in the lower mantle and their modulation of plume formation numerical mantle convection models indicate that subducting slabs can reach the core mantle boundary cmb for a wide range of assumed material properties and plate tectonic histories an increase in lower mantle viscosity a phase transition at 660 km depth depth dependent thermal expansivity and depth dependent thermal diffusivity do not preclude model slabs from reaching the cmb we find that ancient slabs could be associated with lateral temperature anomalies 500 c cooler than ambient mantle plausible increases of thermal conductivity with depth will not cause slabs to diffuse away regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the cmb even for radially simple mantle structures the observation from tomography showing only a few continuous slab like features from the surface to the cmb may be a result of complex plate kinematics not mantle layering there are important consequences of deeply penetrating slabs our models show that plumes preferentially develop on the edge of slabs in areas on the cmb free of slabs plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin however in areas beneath slabs the basal thermal boundary layer would be thicker and plume formation infrequent beneath slabs a substantial amount of hot mantle can be trapped over long periods of time leading to mega plume formation we predict that patches of low seismic velocity may be found beneath large scale high seismic velocity structures at the core mantle boundary we find that the location buoyancy and geochemistry of mega plumes will differ from those plumes forming at the edge of slabs various geophysical and geochemical implications of this finding are discussed

simulations of a quasi taylor state geomagnetic field including polarity reversals on the earth simulator high resolution low viscosity geodynamo simulations have been carried out on the earth simulator one of the fastest supercomputers in a dynamic regime similar to that of earth s core that is in a quasi taylor state our dynamo models exhibit features of the geodynamo not only in spatial and temporal characteristics but also in dynamics polarity reversals occurred when magnetic flux patches at high latitudes moved poleward and disappeared patches with reversed field at low and mid latitudes then moved poleward

mantle plumes link magnetic superchrons to phanerozoic mass depletion events abstract the four most recent large mass extinction events in the phanerozoic the cretaceous tertiary kt the triassic jurassic tj and the permo triassic pt and guadalupian tatarian gt doublet are associated with a major flood basalt eruption with the timing of peak volcanic activity corresponding within measurement uncertainties to the extinction event three magnetic superchrons precede the four largest phanerozoic extinctions the cretaceous long normal superchron duration 35 myr precedes the kt and the permian kiaman long reversed superchron 50 myr precedes the pt gt doublet in addition the newly recognized ordovician moyero long reversed superchron 30 myr precedes the end ordovician extinction event there is a 10 20 myr delay between the end of each superchron and the subsequent mass depletion event both of which represent distant outliers from their respective populations we propose that deep mantle plumes link these seemingly unrelated phenomena long term 200 myr variations in mantle convection possibly associated with the wilson cycle induce temporal and spatial variations in heat flow at the core mantle boundary polarity reversals are frequent when core heat flow is high and infrequent when it is low thermal instabilities in the d layer of the mantle increase core heat flow end the magnetic superchron and generate deep mantle plumes the plumes ascend through the mantle on a 20 myr time scale producing continental flood basalt trap eruptions rapid climatic change and massive faunal depletions

the role of the earth s mantle in controlling the frequency of geomagnetic reversals a series of computer simulations of the earth s dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic field generation in the fluid core eight different patterns of heat flux from the core to the mantle are imposed over the core mantle boundary spontaneous magnetic dipole reversals and excursions occur in seven of these cases although sometimes the field only reverses in the outer part of the core and then quickly reverses back the results suggest correlations among the frequency of reversals the duration over which the reversals occur the magnetic field intensity and the secular variation the case with uniform heat flux at the core mantle boundary appears most earth like this result suggests that variations in heat flux at the core mantle boundary of the earth are smaller than previously thought possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin or because of enhanced heat flux in the mantle s zones of ultra low seismic velocity