crustal reworking at nanga parbat pakistan metamorphic consequences of thermal mechanical coupling facilitated by erosion within the syntaxial bends of the india asia collision the himalaya terminate abruptly in a pair of metamorphic massifs nanga parbat in the west and namche barwa in the east are actively deforming antiformal domes which expose quaternary metamorphic rocks and granites the massifs are transected by major himalayan rivers indus and tsangpo and are loci of deep and rapid exhumation on the basis of velocity and attenuation tomography and microseismic magnetotelluric geochronological petrological structural and geomorphic data we have collected at nanga parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the indus and tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes the localization of this phenomenon at the terminations of the himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics

the role of magma injection in localizing black smoker activity the mechanisms for localization of black smoker systems at mid ocean ridges remain to be fully understood seismic data for a segment of the juan de fuca ridge with long lived black smoker vents reveal ongoing magma recharge into the crustal magma chamber thereby providing an explanation for the localization

tectonic control of yarlung tsangpo gorge revealed by a buried canyon in southern tibet the himalayan mountains are dissected by some of the deepest and most impressive gorges on earth constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region we report here the discovery of a deeply incised canyon of the yarlung tsangpo river at the eastern end of the himalaya which is now buried under more than 500 meters of sediments by reconstructing the former valley bottom and dating sediments at the base of the valley fill we show that steepening of the tsangpo gorge started at about 2 million to 2 5 million years ago as a consequence of an increase in rock uplift rates the high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift

seismic evidence for a hydrothermal layer above the solid roof of the axial magma chamber at the southern east pacific rise a full waveform inversion of two ship wide aperture seismic reflection data from a ridge crest seismic line at the southern east pacific rise indicates that the axial magma chamber here is about 50 m thick is embedded within a solid roof and has a solid floor the 50 60 m thick roof is overlain by a 150 200 m thick low velocity zone that may correspond to a fracture zone that hosts the hydrothermal circulation and the roof itself may be the transition zone separating the magma chamber from circulating fluids furthermore enhanced hydrothermal activity at the sea floor seems to be associated with a fresh supply of magma in the crust from the mantle the presence of the solid floor indicates that at least the upper gabbros of the oceanic lower crust are formed by cooling and crystallization of melt in magma chambers

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

response to comment on tectonic control of yarlung tsangpo gorge revealed by a buried canyon in southern tibet in their comment zeitler et al do not challenge our results or interpretation our study does not disprove coupling between tectonic uplift and erosion but suggests that this coupling cannot be the sole explanation of rapid uplift in the himalayan syntaxes

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

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

207pb 206pb zircon ages and the evolution of the singhbhum craton eastern india an ion microprobe study1this paper is dedicated to prof a k saha one of the senior co authors who passed away after submission of the paper 1 abstract we used an ion microprobe to measure 207 pb 206 pb ages of single zircons from four key lithologies from the singhbhum craton of eastern india detrital zircons from the oldest recognized sedimentary sequence of the craton the older metamorphic group yielded 3 5 3 6 ga ages indicating that crustal formation had already been initiated by 3 6 ga in this region this data also established an older limit of 3 5 ga for the age of sediment deposition the first appearance of extensive continental crust in the singhbhum region marked by the emplacement of the older metamorphic tonalite gneisses is dated at 3 44 ga our data from both of these units reveal that a 3 2 ga event induced overgrowths within each of these pre existing zircon populations we determine an age of 3328 7 ma for the singhbhum granite phase ii the most widespread of this granite s three phases the emplacement of the two phases of the mayurbhanj granite marking the youngest major episode of acid plutonism in this craton took place in rapid succession at 3 1 ga marking the broad scale stabilization of this terrain

transient basin as indicator of tectonic expressions in bedrock landscape approach based on matlab geomorphic tool transient profiler abstract the tectonic and erosional processes sculpture the earth s surface producing a landscape that preserves the evolutionary history of rock uplift and incision the bedrock channels act as an efficient gradation agent where the river profile adjusts to changing tectonic climatic or topological e g river capture boundary conditions and develops a transient basin a suite of slope break knickpoints at comparable elevations in the channel profiles of the transient basin act as important markers we developed a set of comprehensive and interactive matlab tools called a transient profiler to extract the geomorphic indices from the digital elevation model for a basin characterization and landscape evolution period the paleo channel reconstruction from the relict reach in the three studied transient drainage basins palar umiam and dibang suggest a varying surface uplift from 514 1246 and 1981 m with a respective relief gain of 158 230 and 95 respectively we found that the horizontal knickpoint retreat rate is faster in the himalayan thrust system as compared to the shillong pop up system whereas the vertical knickpoint retreat rate is faster in the latter

seismic characterization of an active metamorphic massif nanga parbat pakistan himalaya earthquakes recorded by a dense seismic array at nanga parbat pakistan provide new insight into synorogenic metamorphism and mass flow during mountain building micro seismicity beneath the massif drops off sharply with depth and defines a shallow transition between brittle failure and ductile flow the base of seismicity bows upward mapping a thermal boundary with 3 km of structural relief over a lateral distance of 12 km anom alously low seismic velocities are observed at the core of the massif and extend to depth through the crust the main locus of seismicity and low velocities correlates with a region of high topography rapid exhumation high geothermal gradients young metamorphic and igneous ages and crustal fluid flow we suggest a genetic link between these phenom ena in which hot rocks rapidly advected from depth are pervasively modified at relatively shallow levels in the crust

plio pleistocene exhumation of the eastern himalayan syntaxis and its domal pop up the eastern termination of the himalayan orogen forms a structural syntaxis that is characterised by young from 10 to 7 km in elevation in the core of the syntaxis very high erosion rates documented in sediment downstream of the gorge at the foot of the himalaya contribute 50 of total detritus to the sediment load of the brahmaputra the initiation of very high rates of exhumation has been attributed either to the extreme erosive power of a river flowing across a deforming indentor corner and the associated positive feedback or to the geometry of the indian plate indentor with the corner being thrust beneath the asian plate resulting in buckling which accommodates shortening both processes may be important the northern third of the syntaxis corresponds to a steep domal pop up structure bounded by the india asia suture on three sides and a thrust zone to the south within the dome greater himalaya rocks equilibrated at 800 c and 25 30 km depth during the miocene with these conditions potentially persisting into the latest miocene and possibly the pliocene with modest decompression prior to 4 ma this domal pop up corresponds to the area of youngest bedrock ages on a wide variety of thermochronometers and geochronometers in this paper we review the extensive scientific literature that has focused on the eastern syntaxis and provide new chronological data on its bedrock and erosion products to constrain the age of inception of the very rapid uplift and erosion we then discuss its cause with the ultimate aim to reconstruct the exhumation history of the syntaxis and discuss the tectonic context for its genesis we use zircon and rutile u pb white mica ar ar and zircon fission track dating methods to extract age data from bedrock brahmaputra modern sediments including an extensive compilation of modern detrital chronometry from the eastern himalaya and neogene palaeo brahmaputra deposits of the surma basin bangladesh numerical modelling of heat flow and erosion is also used to model the path of rocks from peak metamorphic conditions of 800 c to 250 c our new data include u pb bedrock rutile ages as young as 1 4 ma from the namche barwa massif and 0 4 ma from the river downstream of the syntaxis combined with existing data our new data and heat flow modelling show that i the detrital age signature of the modern syntaxis is unique within the eastern himalayan region ii the rocks within the domal pop up were 575 75 c only 1 2 myr ago iii the neogene surma basin does not record evidence of the rise and erosion of the domal pop up until latest pliocene pleistocene time iv pleistocene exhumation of the north easternmost part of the syntaxis took place at rates of at least 4 km myr with bedrock erosion of 12 21 km during the last 3 ma v the inception of rapid syntaxial exhumation may have started as early as 7 ma or as late as 3 ma and vi the yarlung tsangpo is antecedent and subsequently distorted by the developing antiform together our data and modelling demonstrate that the domal pop up with its exceptional erosion and topographic relief is likely a pleistocene feature that overprinted earlier structural and metamorphic events typical of himalayan evolution

overview of hydrothermal activity associated with active orogenesis and metamorphism nanga parbat pakistan himalaya the nanga parbat massif is located in northwestern pakistan and occurs in the interior of the western syntaxis of the himalaya recent studies have shown that the massif exposes an active metamorphic anomaly developed in indian plate rocks exhumed from beneath and surrounded by rocks of the kohistan ladakh island arc geochemical and geophysical data from nanga parbat show that an active hydrothermal system exists within the massif in the upper 5 to 6 kilometers of the crust above a shallow brittle ductile transition constrained by microseismic data there is a shallow hydrothermal system with meteoric fluids channelized along active fault zones in contrast below the brittle ductile transition fluids are metamorphic in origin and restricted to unconnected packets along grain boundaries the shallow system is stratified with water rich fluid inclusions near the surface grading to vapor rich inclusions at the brittle ductile transition as evidenced from fluid inclusion studies these fluids are meteoric in origin and enter the massif along shear and fracture zones and exit the massif along the bordering fault zones evidence for these channelized meteoric fluids comes from stable isotopic values of minerals and rocks collected from fault zones that show that these rocks have interacted with meteoric fluids as well as magnetotelluric mt data that show that the fault zones are electrically conductive and embedded in very resistive rocks the deeper portions of the hydrothermal system consist of unconnected metamor phic fluids stable isotopic and fluid inclusion data show that fluids were present during the recent metamorphism but the rocks did not extensively interact with these fluids existence of an unconnected fluid system is supported by the mt studies showing that below the brittle ductile transition the rocks are relatively resistive values ranging from 1000 10 000 ohm m ruling out an interconnected fluid network seismic and mt data also show no evidence of a large magma body at depth we suggest that the type of hydrothermal system observed at nanga parbat can be an important feature of late stage orogenic evolution especially near the tectonically complex edges of orogens the tectonism in these areas exposes deep relatively dry rocks that have previously lost their volatile content during the earliest stages of tectonic thickening and metamorphism these relatively dry rocks are rapidly uplifted and exposed within the massifs where they interact with surface waters at high temperatures and shallow depths

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

can erosion drive tectonics can climate modulated erosion affect the location rate and style of tectonic deformation in earth s crust and thus seismic hazards particularly in the himalaya there are clear correlations between rugged topography and high rates of rainfall erosion and rock uplift 1 2 but a vigorous cause and effect debate continues with new papers presenting evidence for 1 4 and against 5 7 erosional control of tectonics see the figure although much field data are consistent with predicted associations among topography erosion climate and deformation unambiguous evidence has proven elusive 8 by focusing on a simple diagnostic test wang et al show on page 978 1 of this issue 9 that the zone of rugged topography and extreme erosion rates where the tsangpo brahmaputra river cuts through the namche barwa massif see the figure often argued to reflect a dynamic tectonic response to river incision 2 records instead a passive landscape response to tectonics over the past 2 to 2 5 million years the data threaten to undermine one of the most dramatic examples of a proposed tectonic response to erosion 1 lookup volpage 346 978 iss 6212

manganese deposits in the global lithogenetic system quantitative approach abstract a computerized data base including 330 localities and believed to represent at least 95 of the presently recorded spot accumulations of ore grade mn on land is the basis for a quantitative analysis of terrestrial mn resources this file is reprinted in full appendix the present subaerially exposed global ore mn resources are calculated as 17 9 109 t mn 1 in this figure are included the actually mineable straight mn deposits 8 7 109 t mn potentially mineable land based mn accumulations 9 2 109 t mn and actual or potential mn that could be extracted as a byproduct of mining other metals 0 6 109 t mn this distribution is strongly influenced by giant accumulations where the single exceptional kalahari mn field contains over 50 of the presently economic mn ore reserves or 23 42 of the global land mn resources a set of attributes has been selected to treat the global ore mn population in terms of genesis geotectonic and environmental setting and lithologic associations in terms of genesis precipitation from aqueous solutions was responsible for at least 99 of the contemporaneous and probably also the past mn accumulations now exposed on land weathering of mn orebodies has left its mark on 93 of the mn localities and 24 are now represented entirely by supergene assemblages less than 0 01 of the ore mn resources however are formed by weathering related accumulation over silicate rocks ultramafics in terms of geotectonic environments the bulk of the land based mn deposits 97 formed in intraplate and stable continental margin settings 3 1 formed along pacific type and rift type continental margins and only 0 00045 of the deposits formed in an oceanic setting this is in contrast with the outstanding mn accumulating capacity of the present ocean and is a consequence of the low preservation potential of the oceanic domain in terms of lithologic associations 96 of the mn in land based deposits is present in marine sedimentary associations 70 of mn is in banded iron formations 14 4 is in detrital and 11 1 is in carbonate dominated associations chert and jasper limestone sandstone shale and banded iron formation are statistically the most common immediate hosts to mn ores with recorded hosting frequencies of 79 50 45 37 and 35 respectively in terms of geological history the lower proterozoic accounts for 58 9 of the prreserved ore mn on land followed by oligocene 17 2 jurassic 6 2 and middle proterozoic 4 5 in terms of the intensity of mn accumulation per one million years of geological time oligocene 110 106 t mn ma is two orders of magnitude greater than the nearest time periods jurassic 8 9 106 t mn ma and lower proterozoic 6 5 106 t mn ma the historical distribution pattern of the land based mn deposits seems to indicate that accumulation of the bulk of the present ore grade mn is the result of repeated recycling with a land ocean trend abruptly initiated at the time of early cratonization about 2 5 ga this has been supplemented by a substantially less significant but remarkably steady reverse trend of addition of juvenile mn released from the mantle into the crust mafics and particularly basalts are the most important intermediaries in the cumulative secular increase of liberated and accumulated mn in the crust direct to indirect proven to hypothetical spatial coincidence of basalts and mn ores can be demonstrated on at least 169 localities out of 330 51 evaluated

comment on tectonic control of yarlung tsangpo gorge revealed by a buried canyon in southern tibet wang et al reports 21 november 2014 p 978 describe a buried canyon upstream of the yarlung tsangpo gorge and argue that rapid erosion of the gorge was merely a passive response to rapid uplift at 2 5 million years ago ma we view these data as an expected consequence emerging from feedbacks between erosion and crustal rheology active well before 2 5 ma

relationships between hydrothermal activity and axial magma chamber distribution depth and melt content 1 hydrothermal activity especially high temperature discharge is commonly thought to require the presence of an axial magma chamber amc but this association has not been examined systematically the availability of six lengthy 170 560 km ridge sections with continuous surveys of both amcs and hydrothermal plumes now makes it possible to quantitatively compare the distribution and intensity of hydrothermal activity to amc extent depth and at a few locations melt content these six ridge sections span spreading rates from 55 to 145 mm a and total 20 second order segments at the section multisegment scale the linear incidence of hydrothermal plumes increases with amc incidence amci r2 0 64 excluding the hot spot affected galapagos spreading center for all six sections plume incidence increases as amc depth below the seafloor decreases amcz r2 0 66 at the second order segment scale plume incidence is poorly correlated with both amci r2 0 12 and amcz r2 0 25 finally at the subsegment or local scale 0 75 km long bins plume intensity increases as amcz shallows r2 0 85 of bins where plumes are most intense and thus closest to their seafloor sources 68 13 lie directly over an amc as do at least 37 of the 40 known high temperature vent fields the data also allow tests of other hypotheses linking amc properties and hydrothermal activity existing data though still sparse do not support the hypothesis that lenses of melt rich magma preferentially support vigorous long lasting venting also the suggestion that increased hydrothermal cooling within a segment locally depresses amcz finds no support within any ridge section evidence for magma bodies is much scarcer on slow spreading ridges but the data are nevertheless consistent with those from faster ridges observations from all spreading rates thus demonstrate that high temperature vent fields are almost universally associated with the presence or inference of magma hot rock or other nonmagmatic heat sources are insufficient

marine geophysics where there s smoke there s fire seafloor vents spewing mineral rich plumes of hydrothermal fluid termed black smokers can persist at mid ocean ridges for decades or longer earthquake data indicate that ongoing magma injection may determine their locations

the topographic state of fluvially conditioned mountain ranges abstract the topography of mountain ranges reflects the competition of constructive and destructive processes driven by tectonics and climate respectively there is a vital debate whether the topography of individual orogens reflects stages of growth steady state or decay that is fueled by the million year time scales hampering direct observations on landscape evolution the superposition of various process patterns and the complex interactions among different processes hence there is a demand for sophisticated analysis tools to extract constraints on the long term evolution of orogens from their topography we review the field of orogen scale landscape evolution from a numerical perspective summarize the most prominent modelling concepts and their implications for the fluvially driven development of mountain topography and finally evaluate their applicability for understanding real world orogens following the concept of equilibrium a state where uplift rates are balanced by erosion rates and topography remains steady over time the erosional long term response of rivers and hillslopes can be mathematically formalised by the stream power and mass diffusion equations respectively based on a simple 1 dimensional model consisting of two rivers separated by a watershed we explain the influence of uplift rate and rock erodibility on steady state channel profiles and show the time dependent development of the channel drainage divide system dynamic drainage network reorganisation adds additional complexity and its effect on topography is explored on a two dimensional model river capture events and drainage divide migrations as expression of the ongoing drainage network reorganisation cause changes in topography until a stable network topology and hence full topographic steady state is achieved the long time spans needed for this drainage network optimization suggest that orogens on earth may never reach full topographic steady state in real world orogens we find evidence for premature mature and decaying topography as well as relief rejuvenation by analysing slope elevation distributions and trace the expression of crustal strain distorting drainage networks by applying the transform we conclude that modern concepts of landscape evolution allow sophisticated analyses of real world orogens but emphasize that unambiguous results are mostly derived from regions dominated by a limited number of interacting processes such as mountain ranges with limited or no glacial imprint this results in a high demand for techniques to disentangle the complex topography of real world orogens into the signals resulting from the individual land shaping processes

evidence of episodically accelerated denudation on the tibetan namche barwa massif by megafloods abstract megafloods cause widespread mobilization of sediments that have strong potential to control the geodynamic evolution of the namche barwa nb massif by changing the landscape morphology within a short time however the impact of catastrophic events on the denudation of the massif over the longer time scale has not been explored in detail this contribution assesses the impact of catastrophic floods on the denudation style of the namche barwa nb massif over millennial time scales towards this 21 optical ages and 1700 detrital thermochronometric ages of zircon and apatite minerals extracted from paleoflood sediments downstream of the massif were integrated with decadal sediment load and aggradation data to estimate the minimum denudation rate during paleoflood events the results indicate that the 7 ka flood eroded 71 m of material from the nb massif this denudation is equivalent to the material that would be produced over 8000 years of erosion at a rate of 9 mm a the 3 5 ka flood eroded 24 m of material equaling 2500 years worth of erosion at a rate of 9 mm a such relatively instantaneous denudations are three orders of magnitude higher than averaged denudation rates over million year time scale this study therefore provides the first evidence of the strong interplay of catastrophic flood events and tectonics for the rapid exhumation of the namche barwa massif megafloods from the failure of dammed lakes provide valuable information to understand the flood surge risk for human settlements in the siang and the assam valleys

corehole seismometer development for low noise seismic data in a long term seafloor observatory longstanding problems unique to marine seismology in contrast to land based studies include high levels of environmental noise unpredictable instru ment placement short measurement duration and lim ited numbers of instruments traditional instruments are deployed and recovered from a surface ship with no capability to verify data acquisition until the end of the experiment they are often poorly sited and usu ally poorly coupled to the seafloor experiments have typically been short in duration with only a minimum number of instruments the result of these logistical problems is high background noise sparse data recov ery compared to continental stations and low fidelity data in an effort to solve many of these problems we have developed and deployed corehole seismometers 1 90 hz into small boreholes drilled by an underwa ter drilling system using a tethered remotely operated vehicle rov the results are seismic data with a sig nificantly lower background noise level a lower thresh old for recognition of small events well oriented and useable horizontal seismograms and a much longer de ployment capability we present new data from these instruments and compare them with data from two types of traditional instruments deployed from a sur face ship these contemporaneous deployments were conducted during 1996 and 1997 in monterey bay

northward migration of the eastern himalayan syntaxis revealed by osl thermochronometry erosion influences the dynamical evolution of mountains however evidence for the impact of surface processes on tectonics mostly relies on the circumstantial coincidence of rugged topography high stream power erosion and rock uplift using the optically stimulated luminescence osl thermochronometry technique we quantified the spatial and temporal exhumation of the eastern himalayan syntaxis we found increasing exhumation rates within the past million years at the northeast end of the namche barwa gyala peri dome these observations imply headward propagation of erosion in the parlung river suggesting that the locus of high exhumation has migrated northward although surface processes influence exhumation rates they do not necessarily engage in a feedback that sets the location of tectonic deformation

manganese mineralization in archean greenstone belt joda noamundi sector noamundi basin east indian shield abstract a mesoarchean greenstone belt 3 5 3 0 ga in the western part of the east indian shield comprising the iron ore group of the noamundi basin contains economic resources of both iron and manganese ores in the nne plunging regional synclinorium manganese mineralization in the central and eastern parts of this synclinorium particularly in joda noamundi sector has taken place in multiple cycles starting from syngenetic sedimentary and exhalative type through mobilization and remobilization in different stages of tectonism deformation and hydrothermal activities to latest lateritic or supergene type a relatively high temperature metamorphic jacobsite hausmannite bixbyite braunite assemblage low temperature hydrothermal pyrolusite psilomelane hollandite assemblage and supergene pyrolusite manganomelane groutite polianite assemblage are present and were formed by recycling of manganese in different stages of mineralization a detailed structural study of the manganese ore bodies as well as their ore petrographic and mineralogical characteristics with mineral chemistry has revealed systematic mineralization and their relation to deformational phases such recycling of manganese and its structural control of mineralization in different phases is unique of its kind in comparison with other archean manganese deposits in the world

tibetan plateau river incision inhibited by glacial stabilization of the tsangpo gorge much attention has focused on how and when the tibetan plateau formed but far less research has been done on the controls on river incision into the plateau itself oliver korup and david montgomery address this issue which also relates to the question of why the tibetan plateau is still there at all despite hosting one of the deepest gorges on earth the plateau edge is extremely well defined and according to widely accepted stream power theory should be heavily dissected by one of asia s most powerful rivers the yarlung tsangp or yarlung zangbo korup and montgomery propose that the southeastern edge of the plateau was preserved in part by the presence of glaciers that were large enough during the holocene to stall aggressive river downcutting along the plateau margin a considerable amount of research has focused on how and when the tibetan plateau formed in the wake of tectonic convergence between india and asia1 although far less enquiry has addressed the controls on river incision into the plateau itself2 widely accepted theory3 predicts that steep fluvial knick points river reaches with very steep gradients in the eastern himalayan syntaxis at the southeastern plateau margin should erode rapidly4 driving a wave of incision back into the plateau preservation of the plateau edge thus presents something of a conundrum that may be resolved by invoking either differential rock uplift matching erosional decay5 6 7 or other mechanisms for retarding bedrock river incision8 9 in this region where high stream power excludes the potential for aridity as a simple limit to dissection of the plateau10 here we report morphologic evidence showing that quaternary depression of the regional equilibrium line altitude where long term glacier mass gain equals mass loss was sufficient to repeatedly form moraine dams on major rivers such damming substantially impeded river incision into the southeastern edge of the tibetan plateau through the coupled effects of upstream impoundment and interglacial aggradation such glacial stabilization of the resulting highly focused river incision centred on the tsangpo gorge could further contribute to initiating and accentuating a locus of rapid exhumation known as tectonic anaeurysm6

dating the oldest greenstone in india a 3 51 ga precise u pb shrimp zircon age for dacitic lava of the southern iron ore group singhbhum craton abstract this article reports a precise 3506 8 2 3 ma u pb shrimp zircon age for dacitic lava in a well preserved low grade metamorphic and low strained greenstone belt succession of the southern iron ore group singhbhum craton india this age makes the succession the oldest known greenstone belt succession in india and one of the oldest low strain greenstone successions in the world after the 3 51 ga coonterunah group of the pilbara craton western australia and the moderately deformed 3 54 ga theespruit formation of the barberton greenstone belt kaapvaal craton south africa the geochemical composition of the dacitic lava and related volcanic rocks suggests that they formed in a volcanic arc setting the succession also contains a major 120 m thick oxide facies banded iron formation that distinguishes it from the slightly older successions of the pilbara and kaapvaal cratons this banded iron formation may well be one of the oldest and most well preserved and together with associated volcanics

mantle helium reveals southern ocean hydrothermal venting 1 hydrothermal venting along the global mid ocean ridge system plays a major role in cycling elements and energy between the earth s interior and surface we use the distribution of helium isotopes along an oceanic transect at 67 s to identify previously unobserved hydrothermal activity in the pacific sector of the southern ocean combining the geochemical information provided by the helium isotope anomaly with independent hydrographic information from the southern ocean we trace the source of the hydrothermal input to the pacific antarctic ridge south of 55 s one of the major global mid ocean ridge systems which has until now been a blank spot on the global map of hydrothermal venting we identify three complete ridge segments a portion of a fourth segment and two isolated locations on the pacific antarctic ridge between 145 w and 175 w representing 540 km of ridge in total as the potential source of the newly observed plume

spatial and temporal trends in exhumation of the eastern himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the bengal fan the bengal fan provides a neogene record of eastern and central himalaya exhumation we provide the first detrital thermochronological study apatite and rutile u pb mica ar ar zircon fission track of sediment samples collected during international ocean discovery program iodp expedition 354 to the mid bengal fan our data from rutile and zircon fission track thermochronometry show a shift in lag times over the interval 5 59 3 47 ma the oldest sample with a lag time of 6 m y has a depositional age of 5 59 4 50 ma and the zircon and rutile populations then show a static peak until 12 ma this interval from 5 59 4 50 ma to 12 ma is most easily interpreted as recording passive erosion of the greater himalaya however single grains with lag times of 4 m y but with high analytical uncertainty are recorded over this interval for sediments older than 10 ma these grains were derived from the greater himalaya which was exhuming rapidly until ca 14 ma in sediments younger than 10 ma these grains could represent slower yet still rapid exhumation of the syntaxial antiform to the south of the massif lag times 1 m y are again recorded from 14 5 ma to the base of the studied section at 17 ma reflecting a period of greater himalayan rapid exhumation mica 40ar 39ar and apatite u pb data are not sensitive to syntaxial exhumation we ascribe this to the paucity of white mica in syntaxial lithologies and to high levels of common pb resulting in u pb ages associated with unacceptably high uncertainties respectively