kinematics fabrics and geochronology analysis in the medog shear zone eastern himalayan syntaxis abstract the uplift history and tectonic evolution of the eastern himalayan syntaxis ehs have been extensively studied in the last several decades the medog shear zone the eastern boundary of the ehs has preserved considerable significant information on the structural and tectonic evolution of the ehs in this study we report kinematics fabrics and geochronology data of the medog shear zone in the ehs analyses of the crystallographic preferred orientation cpo of quartz ebsd analysis demonstrated that there are three major slip systems 1 basal slip 2 prism c slip and 3 prism slip these slip systems are consistent with microstructures of low temperature shearing medium temperature shearing and high temperature shearing respectively zircons from the two gneiss samples possess inherited magmatic cores and metamorphic overgrown rims yielding a metamorphic age of 29 4 28 6 ma it is suggested that the dextral shearing along the medog shear zone was not earlier than the early oligocene the 40ar 39ar analysis indicates that the medog shear zone experienced three thermo tectonic events from the late oligocene to the pliocene e g 23 4 ma 16 9 12 6 ma and 5 3 ma we correlate the oligocene metamorphic event and the late oligocene to the pliocene multi stage thermo tectonic events that resulted from subduction of the northeast corner of the india plate

petrology of high pressure granulites from the eastern himalayan syntaxis the eastern himalayan syntaxis situated at the eastern terminus of the himalayas is the least known segment of the himalayas recent research in this area has revealed that the syntaxis consists of the gangdise the yarlung zangbo and the himalayan units each of which is bounded by faults the himalayan unit the northernmost exposed part of the indian plate mainly contains amphibolite facies rocks marked by the assemblages staurolite kyanite plagioclase biotite muscovite sillimanite and garnet amphibole plagioclase in the south to the north low to medium pressure granulite grade pelitic gneisses and marbles are present and are characterized by the assemblages garnet sillimanite k feldspar plagioclase or antiperthite biotite quartz spinel cordierite orthopyroxene in gneisses and anorthite diopside wollastonite and plagioclase diopside quartz phlogopite calcite in marbles within this unit the namula thrust system is a series of moderately north dipping structures that displaced the granulite facies rocks southwards over the amphibolite facies rocks high pressure granulites occur as relics within these granulite facies rocks and contain garnet kyanite granulite and garnet clinopyroxenite the peak assemblage of the garnet kyanite granulite includes garnet core part kyanite ternary feldspar quartz rutile sillimanite garnet rim part k feldspar oligoclase ilmenite biotite and spinel albite biotite or spinel cordierite orthopyroxene which are coronas around sillimanite and garnet are retrograde products of this peak assemblage another peak assemblage includes very high ca garnet cao 32 34 wt alm10 grs 80 and diopside cao 22 24 wt scapolite meionite quartz and accessory al bearing titanite al2o3 4 4 5 wt the diopside has kink bands partial or complete breakdown of ca rich garnet during post peak metamorphism produced pseudomorphs and coronas consisting of fine grained symplectic intergrowths of hedenbergite and anorthite thermobarometric estimates in combination with reaction textures mineral compositions and recent experimental studies indicate that these peak assemblages were formed at p c 1 7 1 8 gpa t c 890 c and the retrograde assemblages experienced near isothermal decompression to p 0 5 0 1 gpa t 850 50 c the whole rock compositions indicate that marble and pelite are plausible candidates for the protoliths these facts suggest the following 1 sedimentary rocks were transported to upper mantle depths and equilibrated at those conditions to form these high pressure granulites which were then emplaced into the crust quickly during the rapid exhumation of these rocks the earlier high pressure assemblages were overprinted by the later low to medium pressure assemblages that is the high pressure granulite belt formed in the syntaxis 2 the namula thrust system is an important tectonic boundary in the syntaxis or even in the higher himalaya more generally

contributions of wind forcing waves and surface heating to sea surface height observations in the pacific ocean the dominant processes affecting sea surface height ssh variability observed by the topex poseidon altimeter vary regionally in the pacific baroclinic rossby waves equatorially trapped kelvin waves steric response to seasonal heating and the response to wind stress curl forcing are all important the steric response to surface heating dominates seasonal ssh variability in the subpolar gyre and the eastern subtropical gyre south of the kuroshio extension and south of 20 n in the eastern pacific the dominant contribution to ssh is from near annual period rossby waves to quantify the wave energy observed ssh was assimilated into a kinematic model of westward propagating waves these waves account for 70 of ssh variance between 10 s and 10 n but only 30 between 10 n and 30 n although wave energy in the eastern pacific is correlated with ssh anomalies at the equator the much larger wave energy in the western pacific is correlated with wind stress curl suggesting that the rossby waves there are locally forced in addition to these planetary waves the ocean response to wind forcing via ekman pumping is observed in several places specifically in the north equatorial current a quasi steady topographic sverdrup balance is detectable over most of the north pacific at latitudes as low as 10 15 n as well as in the south pacific where it is seen north of 50 s the decomposition of the ssh signal into propagating waves an ekman pumping response and sverdrup transport is consistent with the results from an isopycnal numerical model

miocene jiali faulting and its implications for tibetan tectonic evolution the karakoram jiali fault zone kjfz comprises a series of right lateral shear zones that southerly bound the eastward extrusion of northern tibet relative to india and stable eurasia here we present new 40 ar 39 ar age data from the puqu and parlung faults two easternmost branches of the jiali fault zone which indicate a main phase of the kjfz shearing from v18 to 12 ma thus the tibetan eastward extrusion bounded by principal strike slip fault zones started and was probably most active around the middle miocene an interval marked also by active east west extension in southern tibet the coincidence of these two tectonic events strongly suggests a common causal mechanism which is best explained as oblique convergence between india and asia under the framework of this mechanism the extension in southern tibet is not a proxy for the plateau uplift the kjfz activity was furthermore coincident with right lateral displacements along the gaoligong and sagaing faults in southeast asia this defines a miocene deformation record for the regional dextral accommodation zone that in response to the continuing india asia collision may have accounted for the initiation and prolonged history of clockwise rotation of the tibetan extrusion around the eastern himalayan syntaxis 2002 elsevier science b v all rights reserved

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

the mesozoic metamorphic magmatic events in the medog area the eastern himalayan syntaxis constraints from zircon u pb geochronology trace elements and hf isotope compositions in granitoids based on the regional geological mapping several granitoid intrusions had been discovered in the eastern himalayan syntaxis ehs in order to constrain their petrogenesis and discuss their relations with the regional tectonics we carried out u pb dating trace elements and hf isotope geochemistry studies on zircons separated from the granitoid rocks in the area of the ehs in this contribution the granitoid rocks are mainly composed of diorites x20 1 6 and granitic gneissic rocks x2 15 1 the u pb zircon dating of diorites yields a crystallization age of 193 8 2 0 ma these zircon have e hf t values ranging from 6 48 to 0 05 indicating an involvement of ancient crustal materials in the generation of these igneous rocks the zircons from the medog granitic gneissic rock commonly show zoning structures the ree patterns and abundances of the inherited cores are different from those of the oscillatory rims the la icp ms u pb zircon in situ analyses indicate that 1 the zircon cores give multi stage magmatic event ages ranging from 516 to 1 826 ma of which six ages are converged on 1 330 911 ma it is considered that the migmatitic gneiss has been formed in this time and 2 while the zircon rims yield 206pb 238u weighted mean ages of 217 4 3 0 ma mswd 3 2 which was interpreted to represent the ages of the triassic anatexis their e hf t values range from 18 98 to 8 36 and 14 22 to 8 72 respectively the timing of the anatexis in the medog area is coeval with the widespread metamorphism in lhasa terrane

observations and controls on the occurrence of inherited zircon in concord type granitoids new hampshire u pb analyses of zircons separated from two concord type plutons near sunapee and dixville notch new hampshire reveal differences in the pattern and magnitude of zircon inheritance which are related to differences in melt chemistry the sunapee pluton contains only slightly more zr than required to saturate the melt at the peak temperature of 700 30 sup 0 c traces of inherited zircon in this separate are inferred to be present as small largely resorbed grains in contrast the long mountain pluton near dixville notch contains about 240 more zr than required to saturate the melt thus more than half of the zr existed as stable inherited zircon crystals during the partial fusion event consistent with the observation of substantial inheritance in all grain size fractions ion probe intra grain analyses of zircon from the long mountain pluton indicate a complex pattern of inheritance with contributions from at least two proterozoic terranes and caution against simple interpretations of upper and lower intercepts of chords containing an inherited component ion probe analyses of zircons from the sunapee pluton reveal clear evidence of u loss which results in incorrect apparent conventional u pb ages ages of crystallization for the long mountain and sunapee pluton are approx more 350 and 354 5 ma respectively a sm nd measurement for the long mountain pluton yields a depleted mantle model age of 1 5 ga consistent with the observed inheritance pattern in contrast a sm nd model age for the sunapee pluton is improbably old due to minor monazite fractionation less

exhumation during crustal folding in the namche barwa syntaxis geological observation in the eastern end of the himalaya shows that the asia india suture is folded metamorphic rocks derived from india occur structurally below the suture in the core of a regional antiform isotopic and fission track dating establish cooling exhumation of rocks from c 30 km depth within the last 4 myr we argue that exhumation is caused by 10 mm yr 1 erosion coeval with crustal scale folding

post glacial entrenchment and knickpoint migration of the yarlung tsangpo gorge southeastern tibetan plateau abstract the formation of the yarlung tsangpo river system is commonly thought to be controlled by tectonic processes initiated several million years ago however climate change may also play an important role in guiding drainage evolution here we reconstruct the drainage history of the yarlung tsangpo gorge using field observations age constraints from optically stimulated luminescence and radiocarbon dating paleosalinity reconstruction and grain size analysis of lacustrine deposits and river valley characteristics field observations clay boron derived paleosalinity reconstruction and grain size analysis of lacustrine deposits demonstrate that a closed inland saline lake existed upstream of the yarlung tsangpo gorge implying that cutting of the gorge postdated this paleolake optically stimulated luminescence and radiocarbon dating suggest that the paleolake formed at least 51 ka and terminated after 13 ka with a shift in global climate following the last glacial maximum the paleolake drained by river capture and the gorge entrenchment commenced at the village of jiala northwest of the namche barwa peak approximately 13 10 ka ago the evolution of the yarlung tsangpo occurred on a remarkably short timescale of just tens of thousands of years in response to drainage system reorganization the yarlung tsangpo incised at an average rate of at least 26 mm yr the rapid fluvial incision initiated at jiala 13 ka ago propagated rapidly upstream at 2 12 m yr the yarlung tsangpo knickpoint has not stabilized but will likely continue to migrate upstream

an empirical evaluation of the argon diffusion geometry in muscovite the temperature time significance of 40ar 39ar muscovite ages is difficult to evaluate quantitatively because of ambiguities in the choice of an appropriate model diffusion geometry the effective diffusion dimension and large uncertainties in experimentally determined diffusion parameters laser 40ar 39ar studies of natural 40ar concentration gradients suggest that argon loss in muscovite occurs primarily via cylindrical volume diffusion commonly with an effective diffusion dimension equal to the crystal diameter the present study tests the cylinder model geometry and the control of physical grain size on the effective diffusion dimension by measuring the anisotropy of a natural40ar diffusion gradient parallel and perpendicular to 001 in a single euhedral muscovite phenocryst the new data combined with previous studies clearly indicate loss of 40ar via cylindrical volume diffusion and strongly suggest that loss of 40ar across the 001 sheets slab diffusion geometry is minimal in undeformed crystals

40ar 39ar dating of the jiali and gaoligong shear zones implications for crustal deformation around the eastern himalayan syntaxis abstract we conducted a comprehensive 40ar 39ar geochronological study of the jiali and gaoligong shear zones to obtain a better understanding of crustal deformation and tectonic evolution around the eastern himalayan syntaxis ehs the new age data reveal that the main phase of deformation in the jiali and gaoligong shear zones occurred from 22 to 11 ma and from 18 to 13 ma respectively structural data collected during this study indicate that the jiali shear zone underwent a change in shear sense from sinistral to dextral during its movement history based on a comparison with the deformation histories of other major shear zones in the region we argue that the initial sinistral motion recorded by the jiali shear zone was coincident with that of the ailao shan red river shear zone which marked the northern boundary of the southeastward extrusion of the indochina block during the early miocene from the middle miocene 18 ma the jiali shear zone changed to dextral displacement becoming linked with the dextral gaoligong shear zone that developed as a consequence of continued northward indentation of the indian continent into asia since this time the jiali and gaoligong shear zones have been united defining the southwestern boundary of the ehs during clockwise rotation of the eastward extruding tibetan block as revealed by recent gps data the temporal change in regional deformation pattern from southeastward block extrusion to clockwise rotation of crustal fragments may have played an important role in the development of the eastern himalayan drainage system around the ehs

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

variability of the north pacific current and its bifurcation abstract the north pacific current npc bifurcates approaching the west coast of north america into a subpolar branch that forms the alaska current and a subtropical branch that includes the california current the variability of this current system is discussed using numerical results from a wind driven reduced gravity model indices of the strength of the subpolar and subtropical components of the npc are examined based on output from multi decadal simulations with the numerical model this shows periods of both correlated and anti correlated variability of the subpolar and subtropical gyres a decomposition of the gyre transport time series indicates that the dominant mode of variability is a breathing mode in which the subpolar and subtropical gyres co vary in response to fluctuations in the strength of the npc this finding is consistent with an analysis of dynamic height data of limited duration from the array of argo drifting floats the variability of the npc is also examined using sea surface height ssh data from satellite altimetry over the period 1993 2005 the leading mode of ssh over the northeast pacific dominates the variability of the npc and is shown to be associated with in phase variations in the transport of the subtropical and subpolar gyres a strong correlation is found between time dependent fluctuations in ssh across the npc and variations in the strength of the transport of the npc in the model this agreement provides evidence for variability of the npc occuring in direct response to large scale atmospheric forcing

thermochronological evidence for the movement of the ailao shan red river shear zone a perspective from vietnam in order to explore the timing of strike slip movement along the ailao shan red river shear zone an 40ar 39ar thermochronological study of the day nui con voi metamorphic massif in northern vietnam was undertaken the massif exposed in the southeastern segment of the ailao shan red river shear zone reveals a rapid cooling in the early miocene 25 21 ma after a very slow cooling ca 34 25 ma the slow cooling period most likely resulted from a geothermal perturbation in the lithosphere owing to the late paleogene 40 30 ma extension in eastern tibet and western yunnan china the rapid cooling consistent with evidence of a wider rapid cooling span from 27 to 17 ma compiled from the entire ailao shan red river shear zone constrains the duration of left lateral shearing which eventually offset indochina from south china by about 600 km the time constraints we have established reinforce the argument that the onset of the ailao shan red river shear zone postdates the opening of the south china sea that began ca 30 ma this result highlights the necessity for reevaluating the cenozoic tectonic models of southeast asia

recent observations of variability in the path and vertical structure of the alaskan stream abstract current records were recently obtained from two sites on the continental slope southwest of kodiak island at the inshore site 10 month record flow mainly resembled the weak shelf break flow typical of the gulf of alaska except for two periods each of 3 months duration the offshore site 31 mouth record was in the path of the alaskan stream during the alaskan stream segments flow characteristics low eddy energy high vertical coherence and high stability were similar to those in the stream at other locations when the stream was absent from the offshore site it made a seaward excursion of 50 km as evidences by satellite tracked drifters the cause of this migration is unclear during a period of 6 months a subsurface velocity maximum was measured at 165 m flow near 1000 m was very weak for almost two years geostrophic flow estimates however suggest this is a rare situation

altimeter derived surface circulation in the large scale ne pacific gyres part 1 seasonal variability abstract the seasonal variability of sea surface height ssh and currents are defined by analysis of altimeter data in the ne pacific ocean over the region from central america to the alaska gyre the results help to clarify questions about the timing of seasonal maxima in the boundary currents as explained below the long term temporal mean of the ssh values must be removed at each spatial point to remove the temporally invariant and large signal caused by the marine geoid we refer to the resulting ssh values which contain all of the temporal variations as the residual ssh our main findings are 1 the maximum surface velocities around the boundaries of the cyclonic alaska gyre the alaska current and the alaska stream occur in winter at the same time that the equatorward california current is weakest or reversed forming the poleward davidson current the maximum surface velocities in the california current occur in summer these seasonal maxima are coincident with the large scale atmospheric wind forcing over each region 2 most of the seasonal variability occurs as strong residuals in alongshore surface currents around the boundaries of the ne pacific basin directly connecting the boundaries of the subpolar gyre the subtropical gyre and the equatorial current system 3 seasonal variability in the surface velocities of the eastward north pacific current west wind drift is weak in comparison to seasonal changes in the surface currents along the boundaries 4 there is an initial appearance next to the coast and offshore migration of seasonal highs and lows in ssh alongshore velocity and eddy kinetic energy eke in the alaska gyre similar to the previously described seasonal offshore migration in the california current 5 the seasonal development of high ssh and poleward current residuals next to the coast appear first off central america and mainland mexico in may june prior to their appearance in the southern part of the california current in july august and their eventual spread around the entire basin in november december similarly low ssh and equatorward transport residuals appear first off central america and mexico in january february before spreading farther north in spring and summer 6 the maximum values of eke occur when each of the boundary currents are maximum

observations from a yakutat eddy in the northern gulf of alaska 1 the impingement of deep basin eddies on the shelf in the gulf of alaska has been implicated as an important mechanism for cross shelf exchange the influence of eddies on biological processes has been confirmed with data from the sea viewing wide field of view sensor showing elevated chlorophyll associated with eddies altimetry data suggest that an eddy formed in the winter of 2003 near yakutat alaska and propagated along the shelf break reaching the head of the gulf by spring this eddy was sampled during may and september of 2003 the eddy core water was warm salty and high in nitrate relative to basin water of the same density but was similar to historical water properties from the shelf near yakutat this suggests a shelf origin for the eddy core water

u pb zircon constraints on the tectonic evolution of southeastern tibet namche barwa area the eastern syntaxis of the himalayas is expressed in the crust as a pronounced southward bend in the orogen the change in strike of geologic features coincides with the high topography of the namche barwa region the exposure of granulite grade metamorphic rocks and a 180 degree bend in the yalu tsangpo we have conducted a geochronologic and geochemical investigation of several suites of granitoids collected from the namche barwa massif and subjacent terranes of southeastern tibet ranging from cm scale dikes and sills to larger outcrop scale intrusions u pb shrimp rg zircon ages establish at least five magmatic episodes 400 to 500 ma 120 ma 40 to 70 ma 18 to 25 ma and 3 to 10 ma these episodes broadly correlate to spatial patterns in sample localities as follows 400 to 500 ma ages occur in zircon cores collected from within the massif proper 120 ma granites related to early gangdese arc plutonism are primarily located northeast of namche barwa later 40 70 ma gangdese activity is expressed in granites west of namche barwa 18 to 25 ma granites occur both along the suture zone west of gyala peri and directly north of namche barwa along the area of the jiali fault zone and are attributed both to shearing within the jiali fault zone and to an early miocene gangdese thrust event exceptionally young 10 ma zircon ages are clustered near the core of the massif along the yalu tsangpo gorge trace element geochemical data indicates the presence of both fluid present and fluid absent melts with a fluid absent decompression melting regime dominating near the core of namche barwa

the nature of the ailao shan red river asrr shear zone constraints from structural microstructural and fabric analyses of metamorphic rocks from the diancang shan ailao shan and day nui con voi massifs abstract the structural geology timing of shearing and tectonic implications of the asrr shear zone one of the most striking lineaments in southeast asia have been the topics of extensive studies over the past few decades the xuelong shan xls diancang shan dcs ailao shan als and day nui con voi dncv metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution our field structural analysis detailed microstructural and fabric analysis as well as the quartz sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during cenozoic tectonic evolution in the shear zone among the contrasting structural and microstructural associations in the shear zone d2 structures which were formed at the brittle to ductile transition during large scale left lateral shearing in the second deformation episode predominate over the structural styles of the other two deformation episodes discrete micro shear zones with intensive grain size reduction compose the characteristic structural style of d2 deformation in addition several types of folds early shearing folds f 2 1 and late shearing folds f 2 2 were formed in the sheared rocks including discrete to distributed mylonitic foliation stretching lineation and shear fabrics e g mica fish domino structures as well as sigma and delta fabrics a sequence of microstructures from syn kinematic magmatic flow high temperature solid state deformation to brittle ductile shearing is well preserved in the syn kinematic leucocratic intrusions deformation structures from the first episode d1 are characterized by f1 folds and distributed foliations s1 in rocks due to pure shearing at high temperatures they are preserved in weakly sheared d2 rocks along the eastern margin of the als belt or in certain low strain tectonic enclaves within the shear zone furthermore semi brittle deformation structures such as hot striae and discrete retrogression zones are attributed to normal slip shearing in the third deformation episode d3 which was probably locally active along the eastern flank of the dcs range for example there are four quartz c axis fabric patterns in the mylonitic rocks including type a point maxima type b y point maxima with crossed girdles superimposition type c quadrant maxima as well as type d point and quadrant maxima combination they are consistent with microscopic observations of microstructures of high temperature pure shearing low temperature simple shearing and their superimposition integrated microstructural analysis and fabric thermometer studies provide information on both high temperature up to 750 c and dominant low temperature 300 600 c deformations of quartz grains in different rock types sillimanite and garnet fabrics especially the latter were primarily formed at the peak metamorphism during high temperature pure shearing the above structural microstructural and fabric associations were generated in the tectonic framework of the indian eurasian collision the low temperature microstructures and fabrics are attributed to left lateral shearing along the asrr shear zone from 27 to 21 ma during the southeastward extrusion of the indochina block which postdated high temperature deformation at the peak metamorphism during the collision

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

the eastern himalayan syntaxis major tectonic domains ophiolitic melanges and geologic evolution abstract geologic mapping in the eastern himalayan syntaxis confirmed the three regional tectonic elements outlined by previous geologic workers our studies however show that the indus yarlung tsangpo suture iys is a continuous melange zone that forms an inverted u in map view around the namche barwa antiform the namche barwa and nyainqentanglha crystalline complexes lie below and above the iys suture respectively and both were parts of the northern indian plate basement rocks with petrologically and geochronologically correlative protoliths both units were deformed metamorphosed and intruded at the end of the proterozoic the zhibai formation the lower part of the namche barwa group extends along the northwest slope of the himalaya and is mainly composed of highly deformed aluminous felsic gneiss containing sporadic boudins of high pressure granulite in the namche barwa antiform the upper part of the namche barwa group includes a calcareous rock assemblage characteristized by marble and diopside bearing calcsilicate rocks interlayed with felsic gneiss petrochemical studies show that the iys contains lenses of oceanic crustal rocks originated from fore arc trench island arc and back arc basin environments which implies they were derived from a ssz type supra subduction zone ophiolite our field mapping identifies the jiali parlung tsangpo remnant suture jps that lies north of the namche barwa antiform as a possible branch of the neo tethyan oceanic realm subduction of the mesozoic neo tethyan oceanic plate resulted in both mesozoic and cenozoic granite intrusions in the northwest trending gangdise magmatic belt along the southern edge of asia uplift and exhumation have been the most recent dominant tectonic processes in the late cenozoic for the high himalayan crystalline rocks namche barwa group in the core of the namche barwa antiform

tectonic evolution of the himalayan syntaxes the view from nanga parbat acknowledgements i was introduced to the himalayas by mike coward in the mid 1980s and remain indebted to him for inspiring a career studying orogenic tectonics i also thank the numerous colleagues both from the uk and from peshawar university who were companions on many field campaigns especially around nanga parbat this contribution has been greatly improved by incisive reviews by tom argles and phaedra upton although of course the author takes full responsibility for the views presented here finally i thank peter treloar for inviting this review and for his patience while i put it together funding over the years this research has been variously supported by the uk s natural environment research council and the royal society published in himalayan tectonics a modern synthesis

timing of granulite facies metamorphism in the eastern himalayan syntaxis and its tectonic implications abstract we present geochronological evidence in the eastern himalayan syntaxis namche barwa for high pressure hp granulite facies metamorphism and explain its importance for understanding both the deep continental subduction of the indian plate beneath asia and its subsequent exhumation the timing of peak and retrograde metamorphism in part constrains these processes but is debated we present zircon u pb and trace element data on granulite facies rocks zircon cores and rims from a weakly retrograded mafic granulite p 14 18 kbar t 800 c yield u pb ages of 24 0 0 3 ma and 18 8 0 3 ma respectively zircon cores and rims from an orthogneiss the host of the mafic granulite yield u pb ages of 490 3 ma and 24 2 0 4 ma respectively an amphibolitized mafic granulite gives a u pb zircon age of 17 0 0 4 ma combined with petrography zircon cl images th u ratios and ree patterns we suggest that the peak metamorphic age for the hp granulite is at 24 ma and subsequent moderate and low pressure retrograde metamorphism occurred at 19 17 ma indicating reasonably rapid exhumation for the hp granulite the ages of detrital zircons from a metasedimentary rock another host rock of the mafic granulite range from 0 6 to 2 0 ga with peak at 0 8 1 2 ga the protolith depositional ages for the metasedimentary rock are constrained to be between 490 and 600 ma our data suggest that the granulite terrane in the eastern himalayan syntaxis has an affinity with the greater himalayan series the hp granulite facies metamorphic events in the eastern himalayan syntaxis are distinct from ultrahigh pressure uhp metamorphic events in the western himalayan syntaxis in both age and depth of burial however the metamorphic history of the eastern and western himalayan syntaxes becomes similar after 24 ma the namche barwa granulites appear to result from the underthrusting of the indian plate lithologies beneath the lhasa block during progressive collisional processes followed by extrusion and or exhumation that result from a slab breakoff of the indian plate during the miocene

sinistral strike slip shearing along the jiali shear zone around the eastern himalaya syntaxis region evidences for oligocene eastward limited translation of tibet abstract in and around the eastern himalaya syntaxis ehs the metamorphic complex and its structural boundaries are key tectonics to investigate the kinematics and thermal evolution of the continental collision we provide new structural kinematic and geochronological data along the northeastern boundary of the ehs namely the jiali strike slip shear zone structures and various kinematic indicators record sinistral strike slip shearing in the zone based on the microstructural features crystallographic preferred orientation patterns of quartz and their slip systems coupled with raman spectroscopy of carbonaceous materials rscm geothermometry the ductile sinistral shearing fabrics formed at upper greenschist and amphibolite facies 500 c two hornblende one muscovite and five biotite separates from the mylonites in the shear zone were dated by the 40ar 39ar method a hornblende plateau age of 23 7 ma is interpreted as representing or being close to the time of sinistral movement muscovite and biotite 40ar 39ar ages from 22 9 to 16 9 ma represent cooling ages following sinistral shearing it is concluded on the basis of these data that the jiali sinistral strike slip shear zone was active in latest oligocene this sinistral movement on the jiali shear zone is considered to link with the ailao shan red river shear zone and form a unique continuous structural boundary around the ehs the jiali ailao shan red river sinistral shear zone and gaoligong dextral shear zone formed a huge conjugate strike slip shear pair around the ehs to accommodate the n s shortening corresponding to northward indentation of the folded indian continent the conjugate strike slip shear systems also contribute to transporting tibet southeastward in a limited scale

differential late cenozoic uplift across the dongjiu milin fault zone in the eastern himalayan syntaxis revealed by low temperature thermochronology abstract the eastern himalayan syntaxis ehs as one of the most tectonically active regions on the earth is one of the best places to explore the relationship between tectonics and surface exhumation process the uplift and exhumation history are often by one of two leading models a stationary or localized tectonic aneurysm or a northeasterly migrating crustal antiform previous researchers have placed great emphasis on the core zone of namche barwa antiform however the dongjiu milin fault zone dmfz which forms the northwestern boundary of the antiform and plays an important role for deformation process in the ehs is still poorly understood in this study we focus on differential late cenozoic uplift across the dmfz we collected 10 bedrock samples in two vertical transects one on the northwest side of the dmfz on the lhasa block and one on the southeast side on the namche barwa antiform and conducted apatite fission track and zircon fission track analyses ten samples collected from the two vertical transects yield aft ages between 3 2 million years ago ma and 10 3 ma and zft ages between 9 9 ma and 12 9 ma a finite element analysis reveals that the two sides of the dmfz have undergone quite different uplift histories and processes in the late cenozoic the lhasa block is uniformly uplifted while the namche barwa antiform is nonuniformly uplifted similar to a buckle fold the phenomenon revealed in this study is best explained by a mechanism whereby the ehs is characterized by the northeasterly migration of an antiform

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

water ice abundance and co2 band strength on the saturnian satellite phoebe from cassini vims observations abstract we have studied the near infrared spectrum of the saturn satellite phoebe a distant satellite observed before cassini s saturn orbit insertion using data from the visual and infrared mapping spectrometer vims on the cassini orbiter we have done a critical calibration of the dataset that involves careful correction of dark artifacts we model areally mixed water ice and non ice assumed segregated because of the low 3 albedo of the non ice material for several high and medium resolution observations of phoebe made near closest approach using a hapke roughness factor of 15 we find ice abundances from 0 1 to over 4 the ice grain radii vary from 1 to 10 m these are displayed on a projected map of phoebe with about 50 coverage about 33 coverage at better than 5 km spatial resolution detailed looks at the water ice spectral fits shows that the weak 1 05 and 1 25 m bands are missing in most of the spectra implying that the ice endmember is not pure ice but has a dark material mixed with it that lowers the albedo and suppresses these bands we made a model of ice contaminated with phoebe like dark material showing that a few percent of dark material lowers the albedo to 50 and suppresses the bands the dirty ice model produces better fits to the spectra and implies that the amount of dirty ice is about 1 5 times the amount of pure ice we have also calculated the co 2 band depth for these same observations and projected the results the co 2 band depth varies inversely with water ice abundance

detrital zircon evidence from burma for reorganization of the eastern himalayan river system the first in situ hf and u pb isotope analyses of detrital zircons from upper miocene sandstone in the inner burma tertiary basin together with data of igneous zircons from the eastern transhimalayan batholith from southern tibet to burma enable us to study the sedimentary source to sink relation and river evolution around the eastern himalayas among 47 out of 62 dated zircons from the miocene sandstone that exhibit cretaceous and paleogene 206pb 238u ages 24 grains have positive ehf t isotope values up to 16 whilst zircons of such ages are common in the transhimalayan plutons those showing high ehf t values have been observed so far only in the gangdese batholith our results therefore support the notion that by late miocene time the yarlu tsangpo which flows past the gangdese batholith in southeastern tibet drained into the irrawaddy river we attribute this river routing to not only regional topographic control but also the dextral movement of the jiali gaoligong sagaing fault system that appears most active during the middle miocene subsequent reorganization of these mountain rivers was affiliated with headward erosion of the brahmaputra river that eventually cut across the namche barwa syntaxis and captured the yarlu tsangpo drainage to form the modern eastern himalayan river system

kinematics and dynamics of the namche barwa syntaxis eastern himalaya constraints from deformation fabrics and geochronology abstract field observations deformation and fabric analyses and precise age data acquired by zircon shrimp la icp ms u pb and 40 ar 39 ar dating methods have yielded new constraints on the kinematics and dynamics of the namche barwa syntaxis nbs which is the eastern corner of the himalaya a two stage model has been established to explain the formation and evolution of the nbs the northward indentation of the indian plate beneath the lhasa terrane began at 55 40 ma and crustal materials at this corner were subducted to depths 70 km where they experienced hp uhp metamorphism since 40 ma large scale right lateral strike slip along the sagaing fault has accommodated the rapid northward movement of the eastern indian plate corner with respect to the indochina block this caused significant and progressive bending of the indus yarlung suture zone iysz such that it became the dongjiu milin left lateral strike slip shear zone dmsz in the west and the aniqiao motuo right lateral strike slip shear zone amsz in the east both zones underwent strong mylonitization meanwhile the hp uhp metamorphic rocks were rapidly exhumed first into the deep crust at 22 18 ma and then to the shallow crust to form an antiformal dome at 6 2 ma our model provides new insight into the processes of post collisional crustal thickening related to the formation of the himalayan orogenic belt

exhumation and topographic evolution of the namche barwa syntaxis eastern himalaya abstract the namche barwa syntaxis as one of the most tectonically active regions remains an appropriate place to explore the relationship between tectonics surface processes and landscape evolution two leading models have been proposed for the formation and evolution of this syntaxis including the tectonic aneurysm model and the syntaxis expansion model here we use a multi disciplinary approach based on low temperature thermochronometry numerical modeling river profile and topographic analyses to investigate the interactions between tectonics erosion and landscape evolution and to test these models our results emphasize the presence of young cooling ages i e

interannual variability in northeast pacific circulation 1 interannual variability of the circulation in the northeast pacific ocean is explored through a joint analysis of expendable bathythermograph xbt and expendable conductivity temperature depth xctd data satellite altimetry and output from a model that was constrained by ocean data xbt temperature profiles with high spatial resolution are available in the eastern north pacific along two repeated transects these ship tracks along with the coast of north america define a closed box which is used to study the time mean circulation and its variability on interannual timescales geostrophic velocities from xbt data are compared with geostrophic velocities from model output as well as the full model velocity fields correlations in variability on interannual timescales between transport in the subpolar gyre and in the subtropical gyre are present in both model output and data the nature of the variability and its relation to the changes of the strength of the north pacific current npc which supplies the water for both gyres are explored interannual variability in gyre transport is found to be related to both the bifurcation of the npc resulting in an anticorrelation in transport between the two gyres and to variations in npc strength resulting in simultaneous changes in the two gyres the dominant signal is found to be a long term increase in the npc which results in a strengthening of the subtropical gyre possible connections with local scale wind stress changes and with the el nino southern oscillation phenomenon are also explored

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

the namche barwa syntaxis evidence for exhumation related to compressional crustal folding abstract geological observation in the eastern end of the himalayas shows that the asia india suture is folded and continues southward into india and burma where the continuation of the transhimalayan plutonic complex can be identified metamorphic rocks derived from india occur structurally below the suture in the core of a regional antiform isotopic and fission track dating are consistent with the geological interpretation in addition they establish cooling exhumation of rocks from c 30 km depth within the last 4 ma rapid exhumation of deep crustal levels in mountain systems is generally related to extension subsequent to thermal softening of a thickened continental lithosphere however in the eastern himalayas we argue that exhumation is caused by c 10 mm yr 1 erosion coeval with crustal scale folding the general history of this syntaxis resembles the evolution of the western himalayas syntaxis in pakistan

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

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

altimeter derived surface circulation in the large scale ne pacific gyres part 2 1997 1998 el nino anomalies abstract changes in the sea surface heights ssh and geostrophic transports in the ne pacific are examined during the 1997 1998 el nino using altimeter data sea level pressure slp fields proxy winds and satellite sea surface temperature sst most of the signal occurs along the boundaries of the basin from panama to the alaska peninsula changes in the ssh and alongshore transports along the boundaries are caused both by propagation of signals from the south stronger between the equator and the gulf of california and by local and basin scale winds stronger between the pacific northwest and the alaska peninsula two periods of high ssh occur at the equator may july 1997 and october 1997 january 1998 the first coastal ssh signal moved quickly polewards to approximately 24 n in early june then stalled and moved farther north during transient events in july september large scale wind forcing combined with the equatorial signals during the second period of high equatorial ssh fall 1997 to move the high ssh and poleward transports quickly around the alaska gyre a connection between the boundary currents and the interior north pacific developed as part of the large scale response to the basin scale winds after changes in the boundaries decreases in anomalies of ssh and poleward transports began in january 1998 south of 40 n and in february 1998 farther north

mid eocene high sr y granites in the northern himalayan gneiss domes melting thickened lower continental crust abstract within the himalayan collisional belt granotoids occur along two sub parallel belts the northern himalayan gneiss domes nhgd and the high himalayan crystalline series hhcs in the yardoi area of nhgd two mica granite a new type granite occurs in the core of the yardoi gneiss dome ygd dala and quedang from north to south and extends at least 50 km long these granites have similar mineral composition elemental and radiogenic isotope geochemistry and age of formation shrimp zircon u pb dating indicates that the yardoi and the quedang two mica granites formed at 42 6 1 1 ma and 42 8 0 6 ma respectively similar to the dala pluton these two mica granites have 1 high sio2 68 wt al2o3 15 wt and a cnk 1 0 2 relatively high sr and lree but low y 40 and up to 250 and la yb 30 4 very weak or no eu anomalies and 5 as compared with those in the himalayan leucogranites low initial sr 87sr 86sr i

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

a regional index of northeast pacific variability based on satellite altimeter data 1 an index of climate variability to monitor the state of the upper ocean is proposed for the northeast ne pacific ocean based on sea surface height ssh data from satellite altimetry while sea surface temperature sst is often used characterize ocean variability ssh reflects the integrated influence of temperature and salinity anomalies through the water column a canonical correlation analysis shows that ssh and sst anomalies vary coherently at large spatial scales and low frequencies over the region ssh anomalies are less subject to short period variability and the temporal components for ssh resemble smoothed low pass filtered versions of the sst components also examined is the relationship between the sst based pacific decadal oscillation pdo index and the large scale upper ocean variability reflected in the leading principal component of ssh anomalies the comparison demonstrates that the ssh principal component provides a robust index of regional climate variability that is less noisy than the pdo the results are used to examine the 1998 2002 climate event over the ne pacific

effect of crystal preferred orientations on the thermal diffusivity of quartz polycrystalline aggregates at high temperature article i nfo thermal diffusivity of synthetic quartz single crystals and natural polycrystalline aggregates were measured using a modified angstrom method at ambient pressure and up to 800 c in order to investigate the effect of crystal preferred orientation on thermal diffusivityof quartz rich rocks the thermal diffusivitytensorof quartz was determined by measuring the thermal diffusivity of an oriented synthetic quartz single crystal along the 100 and 001 directions a naturally deformed fine grained quartzite mylonite was used to compare the single crystalproperties with aggregate properties using thecrystal preferred orientations cpo measuredby the electron back scattered diffraction ebsd method and the measured thermal diffusivity tensor of quartz the three dimensional aggregate thermal diffusivity was modelled using volume averaging models in order to test the validity of these models that are only based on the properties of the constituent minerals the thermal diffusivity was then measured on oriented cores as a function of temperature along three orthogonal directions parallel to the x lineation y z pole to foliation structural frame both modelled and direct measurement of thermal diffusivity show an anisotropy of thermal diffusivity heat transport being more effective parallel to y direction and less effective parallel to the lineation x direction thermal diffusivities measured in a given direction on the natural rock are lower by less than 10 than the modelled thermal diffusivity in the same direction showing that rock imperfections have a weak effect on heat transport in addition the modelled thermal diffusivity anisotropy based on the characterization of crystal orientations and thermal diffusivity tensor shows a good agreement with measurements in both and stability field this validation of the petrophysical simulation allows for evaluating the 3d thermal diffusivity of quartz rich rocks in different crustal conditions the 3d thermal diffusivity of five naturally deformed quartzites displaying quartz fabrics expected in different crustal pressure and temperature ranges were simulated the resulting thermal diffusivity anisotropies of quartzites range between 40 and 10 depending on temperature crystallographic fabric patterns and fabric strength under crustal conditions quartzites deformed in the granulite facies display a high thermal diffusivity in the xz foliation plane whereas quartzites deformed in greenschist facies have highest thermal diffusivity in the z direction normal to the foliation plane

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

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties