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

boiling fluids in a region of rapid uplift nanga parbat massif pakistan abstract the nanga parbat massif of northern pakistan is currently undergoing rapid uplift 5 10 mm a 1 resulting in near surface elevated temperatures numerous quartz veins cut geologically young structures 100 c km 1 and the isotherms describe a giant pillar of heat above about 4 km fluid temperature is greater than conductive rock temperature in permeable zones which carry convecting boiling meteoric fluid

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

identification of inherited radiogenic pb in monazite and its implications for u pb systematics the simplest interpretation of uranium lead mineral ages in igneous rocks embodies the assumption that melting of pre existing rocks leads to homogenization of the lead isotopes thus resetting the radiometric clock zircons often violate this assumption by only partially dissolving and preserving a component of lead inherited from before the melting episode but until now such behaviour has not been observed in monazite here we report u pb data for zircons and monazites from a tertiary granite from the himalayas in which zircons and monazites contain inherited radio genic lead an analysis of a single entirely igneous zircon crystal plots on concordia at 19 5 0 4 myr eight monazite fractions lie on a line from an upper intercept of 471 10 myr to the youngest fraction which plots slightly above concordia at 21 myr the presence of excess 206pb in the youngest monazite fractions indi cates that the monazite data represent a mixing line between young magmatic monazite and an older inherited component rather than a resetting of 471 myr monazites at 20 myr these data suggest a closure temperature for pb in monazite significantly higher than previously published estimates

assessing the extreme overwash regime along an embayed urban beach abstract coastal overwash is one of the most important hazards affecting the coastal zone and therefore has been the focus of several studies related to the establishment of setback lines however studies of extreme overwash eo events along urban beaches backed by a seawall or structure are scarce and reveal the difficulties associated with its assessment measurement and validation the nazare coastal urban area located on the west coast of portugal is developed adjacent to an embayed reflective beach and is subject to frequent and localized inundation due to eo events capable of overtopping the protection seawall the current work develops a methodological approach to simulate total water levels twl and seawall overtopping occurrences in time and space with the ultimate goal of identifying the factors that govern the extreme overwash regime the method uses multi decadal time series of site specific wave and tide and high resolution topo bathymetric data and recreates the twl time series for a 36 year period the model is successfully validated against video imagery and maximum swash line data that provide information on the reach of the water levels measured during modal and extreme twl conditions along the studied beach this study establishes the importance of the interaction of the modal and extreme hydrodynamic processes with the beach and backshore morphology the nazare embayment is in equilibrium with the alongshore varying modal wave conditions resulting in higher vulnerability of the most sheltered sector during extreme events

on the inference of denudation rates from cooling ages of minerals abstract the inference of denudation rates from the temperature time histories of rocks is not straightforward because the geothermal gradient evolves with time as denudation advects heat towards the land surface we show that the curvature in the temperature time path recorded by an exhumed rock is strongly dependent upon denudation rate and upon the temperature of the rock before denudation began but only weakly dependent upon the initial geothermal gradient the original depth of burial of the rock or the duration of the denudation for the case in which denudation rate is constant a systematic search of parameter space yields robust estimates of denudation rate and of the initial temperature if there is prior knowledge of the initial geothermal gradient the original depth of burial of the rock or the duration of the denudation this may be used further to limit the acceptable ranges of the other two parameters application of this procedure to two geological examples suggests that denudation rates in the nanga parbat massif are lower and less variable than previously suggested and that the inference drawn from accelerated cooling rates of accelerating denudation in the andes is incorrect

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

isotope studies reveal a complete himalayan section in the nanga parbat syntaxis many models of orogenesis invoke simple anatomies for mountain belts comprising a small number of major tectonic provinces separated by major faults in the himalayan arc three main tectonic provinces the lesser himalayan high himalayan and tethyan series have been recognized over 2500 km along strike from bhutan to kashmir however their extension westward to the nanga parbat syntaxis remains equivocal we have supplemented detailed field work in the area with isotopic analysis aimed at revealing distinct signatures for each of the three main provinces using sr isotopic data to refine previous nd based discrimination we demonstrate that the three main tectonic provinces of the central himalaya also occur in the western syntaxis of northern pakistan these three units are thus continuous along the entire orogenic arc however their metamorphic grade is generally higher in the syntaxis than in the central himalaya challenging the validity of distinctions commonly drawn on this basis elsewhere in the mountain belt the corollary is that these high grade units probably continue beyond the syntaxis into northwestern pakistan which suggests that although the precollisional materials may be identical the western syntaxis marks a change in tectonic style from the main orogen this conclusion in turn requires that the burial and exhumation history in the western himalaya be radically different from that in the central himalaya and thus necessitates a reexamination of models for india asia collision

nd and pb isotope variability in the indus river system implications for sediment provenance and crustal heterogeneity in the western himalaya abstract the indus river system is the only major drainage system in the western himalaya and erodes not only the high himalaya but also topographically high regions within and north of the indus suture zone most notably the karakoram ion microprobe analysis of pb isotopes in detrital k feldspar grains taken from the tributaries of the indus together with bulk nd isotope analysis of those same sediments is here used to identify distinct sediment source regions these span the very radiogenic nanga parbat and associated lesser himalaya the relatively radiogenic intermediate high himalaya the unradiogenic ladakh and kohistan batholiths and intermediate values in the hindu kush karakoram and lhasa block the range of compositions reflects differing degrees of recycling of older continental crust during petrogenesis k feldspars from the ladakh and kohistan batholiths are less radiogenic than the laterally equivalent gangdese granite of tibet interpreted to reflect the preferential recycling of accreted oceanic arc units within the western transhimalaya prior to india asia collision similarly the zanskar high himalaya are less radiogenic than their equivalents in nepal isotope values from pleistocene indus fan sediment are compatible with a dominant source in the karakoram with additional important contributions from the arc batholiths and high himalaya reflecting both the area and modern rates of tectonic uplift within the drainage basin in contrast radiogenic grains are common in the lower reaches of the modern indus river possibly as a result of the damming of the main river channel where it reaches the foreland

from sediment to granite timescales of anatexis in the upper crust abstract granite formation is the culmination of a sequence of events initiated by prograde heating of the protolith and followed by formation of a grain boundary melt melt segregation into a vein network ascent of the melt through the network and finally crystallisation of the melt experimental constraints on the formation of a crustal melt from the incongruent melting of muscovite combined with geochemical studies of anatexis in the high himalaya allow the timescales required for each of these processes to be assessed discordant temperatures determined from monazite and zircon thermometry for himalayan anatectic granites indicate that at least for some intrusives the melt was undersaturated in lree implying that melts have probably been extracted in less than 10 ka experimental studies suggest that some himalayan melts are also undersaturated in zr implying segregation may have occurred within 100 years such short timescales confirm that deformation driven mechanisms are important in extracting these melts from their source the transport distances of himalayan granitic melts of 10 km may be achieved by the ascent of magma through dykes in about 1 day at such rates even the largest granite could theoretically be emplaced in 10 years crystallisation of himalayan melts involves much longer periods if emplaced as thin sheets 100 m wide a timescale of 500 years is required compared with 30 ka for single stage intrusion of the larger laccoliths for composite sheet complexes magma crystallisation rather than melt ascent comprises the rate determining step on the emplacement of the intrusion the overall timescales of melt segregation and emplacement for many orogenic granites are therefore less than 10 ka and possibly less than 1 ka in contrast the timescale required for prograde heating of the protolith is 1 ma since the melt production rate is determined by heat flow into the protolith and not by reaction kinetics for any geologically significant period we conclude that heat flow determined by both the mechanism of heating and the thermal diffusivities of crustal rocks provides the overall rate determining step of crustal anatexis

himalayan metamorphism and its tectonic implications the himalayan range exposes a spectacular assemblage of metamorphic rocks from the mid and deep crust that have fostered numerous models of how the crust responds to continental collisions recent petrogenetically based petrologic and geochronologic studies elucidate processes with unprecedented resolution and critically test models that range from continuum processes to one time events the pronounced metamorphic inversion across the main central thrust reflects continuum thrusting between ca 15 and 20 ma whereas exposure of ultrahigh pressure rocks in northwestern massifs and syntaxis granulites reflects singular early 45 ma and late 10 ma exhumation events multiple mechanisms including wedge collapse and flow of melt weakened midcrust are debated to explain pressure temperature trajectories patterns of thinning and thermal overprinting a geochronologic revolution is under way in which spatially resolved compositions and ages of accessory minerals are combined in a petrogenetically valid co

documentation of neogene regional metamorphism in the himalayas of pakistan using u pb in monazite abstract in the himalayas investigators have constrained the timing of metamorphism associated with the eocene orogeny through the use of cooling ages on a number of minerals the majority of such studies give minimum metamorphic ages of 30 40 ma 1 2 3 4 5 6 largely confirming theoretical studies predicting peak metamorphic conditions occurring tens of millions of years after large scale collision e g 7 in northwestern pakistan however the nanga parbat haramosh massif nphm exhibits much more recent activity with rapid and accelerating cooling over the past 10 ma 1 2 the nphm also exhibits unexpectedly recent igneous activity three leucogranite dikes give minimum zircon u pb ages of 7 5 and 2 3 ma 8 the problem we address in this paper is whether the thermal structure suggested by recent leucogranite production at depth is discernible in the shallower metamorphic rocks of the nphm to date metamorphism we have used the u th pb system in monazite a common accessory mineral in high grade metamorphic rocks which can be a viable metamorphic geochronometer dating the formation of the mineral under moderate metamorphic conditions 9 10 monazite separated from schists and gneisses of the nphm gives u pb ages of 4 11 ma we interpret these young ages as evidence for neogene metamorphism affecting the nphm an event heretofore unsuspected in the greater himalaya and only intimated in the nphm this recent metamorphism roughly coincided with leucogranite production at depth 8 and with the onset of high denudation rates 1 2 as such our conclusions offer important constraints on further modeling of similarly anomalous behavior within tectonically active regions suggesting that any reasonable model should strive to explain the relationship between recent rapid uplift and coincident recent metamorphism

extreme value statistics for wave run up on a natural beach abstract statistics of wave run up maxima have been calculated for 149 35 minutes data runs from a natural beach during the experiment incident wave height varied from 0 4 to 4 0 m incident wave period from 6 to 16 s and beach face slope from 0 07 to 0 20 four extreme statistics were calculated the maximum run up height during each run the 2 exceedence level of shoreline elevation the 2 exceedence height for individual run up peaks and the 2 exceedence level for swash height as determined by the zero upcrossing method these statistics were best parameterized when normalized by the incident significant wave height and plotted against the iribarren number h l 0 1 2 the swash data with set up removed showed less scatter than total run up with set up included for iribarren number greater than 1 5 the run up was dominated by the incident frequencies for lower iribarren number longer period motions dominated the swash a reasonable value of wave steepness for a fully developed storm sea is 0 025 so that a storm iribarren number can be estimated as 6 3 times the beach slope using this and an offshore design wave height the included graphs may provide guidance in determining a design run up height

improving constraints on apatite provenance nd measurement on fission track dated grains detrital thermochronology is commonly used to locate source and improve the understanding of a region s long term development provenance detrital age data typically comprise a number of distinct age modes representing contributions from a number of different sources for methods such as apatite fission track ft this can present a challenge in that direct assignment of age modes to particular lithological or tectono stratigraphic units is rarely possible particularly when ancient orogenic sediments are examined a new approach described here is based on measuring nd isotopic data on single apatites by laser ablation icpms where the 143nd 144nd ratios are diagnostic of grain source by combining nd isotopic measurement with apatite ft analysis it is possible to link detrital apatite ft ages to specific rock unit sources the methodology and wider benefits of this new approach are discussed using examples from the himalaya and andaman islands geological society of london 2009

modelling storm impacts on beaches dunes and barrier islands a new nearshore numerical model approach to assess the natural coastal response during time varying storm and hurricane conditions including dune erosion overwash and breaching is validated with a series of analytical laboratory and field test cases innovations include a non stationary wave driver with directional spreading to account for wave group generated surf and swash motions and an avalanching mechanism providing a smooth and robust solution for slumping of sand during dune erosion the model performs well in different situations including dune erosion overwash and breaching with specific emphasis on swash dynamics avalanching and 2dh effects these situations are all modelled using a standard set of parameter settings the results show the importance of infragravity waves in extending the reach of the resolved processes to the dune front the simple approach to account for slumping of the dune face by avalanching makes the model easily applicable in two dimensions and applying the same settings good results are obtained both for dune erosion and breaching

conflicting zircon vs titanite u pb age systematics and the deposition of the host volcanic sequence to kiruna type and iocg deposits in northern sweden fennoscandian shield abstract the northern norrbotten region and in particular the kiruna area hosts a number of large apatite iron oxide deposits e g the huge kiirunavaara ore of significant economic importance age data from rock lithologies hosting these ores represented by metamorphosed rocks of the porphyrite and kiirunavaara groups are complex to interpret this is illustrated by la icp ms data for titanite and to some extent for rutile which scatter considerably yielding ages within a span from ca 2 1 ga to 1 7 ga these analysed hydrothermal minerals characterized by complex bse images revealing darker and brighter zones are located in ore zones and associated with e g strong scapolitisation albitisation and actinolitisation previous tims zircon ages of host rocks on the other hand define a more narrower age interval between ca 1900 and 1870 ma and this is supported by new u pb zircon results presented here furthermore one coherent set of sims data for titanite from the luossavaara ore favour that crystallization took place at ca 1 88 ga although laser icp data from the same locality are much more complex an implication arising from published pre 1 9 ga laser ablation ages for titanites is that the emplacement of host rocks started already at around 2 1 ga as the depositional time of these rocks is crucial for the understanding of the overall crustal formation in northern norrbotten additional rocks were selected for age dating new zircon age data la icp ms and sims give support to a scenario where host rocks to ores started to develop at around 1900 ma and this calls for a re evaluation of published la icp ms data of hydrothermal mineral phases here we present four models that aim to explain how pre 1 9 ga titanite ages believed to have a questionable geological significance may develop the principal idea is that 2 1 ga alteration events were not responsible for the crystallization of the hydrothermal minerals instead it is believed that apparent old age domains carry excess radiogenic lead due to the effect of 1 9 ga hydrothermal processes currently the interpretation of u pb isotope data in the study area remains enigmatic and further radiometric analyses are required

viscous heating allows thrusting to overcome crustal scale buckling numerical investigation with application to the himalayan syntaxes article i nfo the eastern and western himalayan syntaxes are crustal scale antiforms whose metamorphic evolution is coeval in the india asia collisional history finite element modelling of lithospheric shortening and the resultingcrustal scale folds havepreviously been used todebate the structuralconditions for the development of such structures however numerical models could not account for the metamorphic evolution associated with folding in continuation of previous work we present two dimensional finite element modelling of lithospheric shortening inwhich thermal effects are implemented the new models are consistent with earlier interpretations that crustal folding is the plausible mechanism that shaped the two himalayan syntaxes they further lend support to the concept that lithospheric buckling is a basic response to large scale continental shorteningandan efficientmountainbuilding process introducingviscous shearheating shows however that the buckling mode shifts to a thrusting mode within few shortening depending on the initial thermal rheological structure of the deforming lithosphere the change to the thrusting mode prohibits further fold amplification and lateral fold propagation this mayexplainwhy in continental lithosphere crustal scale folds are isolated whereas regular periodic crustal fold trains are rare focusing deformation on through limbs thrust zones accompanies the establishment of inverted metamorphic gradients these results offer new working hypotheseson howlargethrusts like thehimalayamain centralthrustnucleate results further show that the thermal structure of the lithosphere strongly controls three fundamental deformation and metamorphic modes 1 a cold lithosphere mainly deforms by thermally activated thrusting and exhibits large areas with significant tectonic overpressures twice lithostatic 2 a warm lithosphere is essentially buckled and significant tectonic overpressure builds up in the upper crust and 3 a hot lithosphere tends to thicken homogenously and mainly records lithostatic pressures below the upper crust

two dimensional time dependent hurricane overwash and erosion modeling at santa rosa island abstract a 2dh numerical model which is capable of computing nearshore circulation and morphodynamics including dune erosion breaching and overwash is used to simulate overwash caused by hurricane ivan 2004 on a barrier island the model is forced using parametric wave and surge time series based on field data and large scale numerical model results the model predicted beach face and dune erosion reasonably well as well as the development of washover fans furthermore the model demonstrated considerable quantitative skill upwards of 66 of variance explained maximum bias 0 21 m in hindcasting the post storm shape and elevation of the subaerial barrier island when a sheet flow sediment transport limiter was applied the prediction skill ranged between 0 66 and 0 77 in a series of sensitivity tests in which several hydraulic forcing parameters were varied the sensitivity studies showed that the variations in the incident wave height and wave period affected the entire simulated island morphology while variations in the surge level gradient between the ocean and back barrier bay affected the amount of deposition on the back barrier and in the back barrier bay the model sensitivity to the sheet flow sediment transport limiter which served as a proxy for unknown factors controlling the resistance to erosion was significantly greater than the sensitivity to the hydraulic forcing parameters if no limiter was applied the simulated morphological response of the barrier island was an order of magnitude greater than the measured morphological response

valley incision and the uplift of mountain peaks simple end member models describe the effect of isostatically compensated valley incision on the elevation of mountain peaks these models allow calculation of the maximum portion of mountain peak elevations attributable to the development of observed relief and predict general downstream patterns of ridgetop uplift in response to erosion by fluvial processes analyses of topographic profiles across major drainages of the central sierra nevada and the tibetan plateau indicate that isostatically compensated valley incision could account for at most 5 10 of the present elevation of mountain peaks in contrast analyses of topographic profiles across the himalaya show that as much as 20 30 of the present elevation of himalayan peaks could be explained by isostatically compensated valley incision the degree to which valley incision is compensated locally however depends on the flexural rigidity of the lithosphere the size of the range and its tectonic boundary conditions these results show that while a tectonic control is required for late cenozoic surface uplift of the sierra nevada a significant portion of the elevation of himalayan peaks may reflect late cenozoic valley incision on the margin of the tibetan plateau

variations in parameters of extreme value distributions of water level along the eastern baltic sea coast abstract time series of water level at several sites of the eastern baltic sea contain statistically almost impossible outliers their presence may considerably modify the appearance of the relevant extreme value distributions we analyse systematically the variation in the parameters of the generalised extreme value gev gumbel and weibull distributions for extreme water levels along a 600 km coastal stretch in the north eastern baltic sea the parameters of the distributions are evaluated using a three different methods b the output of two different ocean models and c two versions of block maxima for calendar years and for stormy seasons and compared with similar parameters retrieved for measured water level time series at five sites the location and scale parameters of gev and gumbel distributions vary smoothly by about 30 from their average values the variation is modest along the open shores of the baltic sea proper all these parameters increase almost linearly along the southern coast of the gulf of finland the absolute values of the shape parameter of the gev distribution are mostly

fission track evidence for quaternary uplift of the nanga parbat region pakistan the north striking nanga parbat haramosh massif protrudes into the northwestern himalaya along the axis of a great syntaxis1 2 fig 1 where the hindu kush karakorum and himalayan ranges converge as the indus suture zone3 enters this region from the east it bifurcates into two branches encircling what may be a docked island arc terrane4 the southern branch the main mantle thrust crops out on both flanks of the nanga parbat massif forming a tight structural loop5 this massif and the adjacent terrane contain some of the highest peaks in the himalaya nanga parbat and the indus river located just 20km away define the world s greatest continental relief 6 930 m we report here the discovery of unexpectedly young sphene zircon and apatite fission track dates from the nanga parbat haramosh massif these dates as low as 1 3 myr for zircon and 0 4 myr for apatite imply that during the pleistocene the nanga parbat region was uplifted and eroded at nearly 1 cm yr 1

apatite fission track and u th he ages from the higher himalayan crystallines kaghan valley pakistan implications for an eocene plateau and oligocene to pliocene exhumation abstract apatite fission track and apatite and zircon u th he ages were obtained from high and ultra high pressure rocks from the kaghan valley pakistan four samples from the high altitude northern parts of the valley yielded apatite fission track ages between 24 5 3 7 and 15 6 2 1 ma and apatite u th he ages between 21 0 0 6 and 5 3 0 2 ma these data record cooling of the formerly deeply subducted high grade metamorphic rocks induced by denudation and exhumation consistent with extension and back sliding along the reactivated normal acting main mantle thrust overlap at around 10 ma between fission track and u th he ages is recognised at one location besal showing that fast cooling occurred due to brittle reactivation of a former thrust fault widespread miocene cooling is also evident in adjacent areas to the west deosai plateau tso morari most likely related to uplift and unroofing linked to continued underplating of the indian lower crust beneath ladakh and kohistan in the late eocene to oligocene in the southernmost part of the study area near naran two significantly younger late miocene to pliocene apatite fission track ages of 7 6 2 1 to 4 0 0 5 ma suggest a spatial and temporal separation of exhumation processes these younger ages are best explained by enhanced late miocene uplift and erosion driven by thrusting along the main boundary thrust

tracing the fluid evolution of the kiruna iron oxide apatite deposits using zircon monazite and whole rock trace elements and isotopic studies the ore genesis of the paleoproterozoic iron oxide apatite deposits in the vicinity of kiruna in northern sweden is poorly understood despite a century long mining history and 2500 mt of iron ore with grades of 30 to 70 wt fe produced in the region to date zircon grains from the ore recently dated at ca 1874 ma show very different appearances compared to zircon from surrounding host rocks ca 1880 ma and related intrusions ca 1880 and ca 1874 ma particularly an inclusion rich rim in contrast zircon from the host rocks and a proximal granite intrusion exhibit typical igneous growth zoning electron microprobe results show near stoichiometric composition for zr si and hf in the host rock zircon grains the ore zircon crystals have low analytical totals with significant concentrations of ca fe y and p and infrared spectroscopy showed several weight percent of water these ore zircon grains further show fe rich inclusions zones and or veins in elemental x ray maps and light rare earth elements lree enrichment transmission electron microscopy tem shows that the lree are not due to micro or nano inclusions in the zircon but are likely hosted as lree oxides in amorphous regions of the grains based on these characteristics the rims on ore zircon grains are interpreted to be of hydrothermal origin uranium pb in monazite from the ore measured by sims suggests a secondary event influencing the area at ca 1624 ma a period of known geologic activity in fennoscandia electron microprobe x ray mapping of these monazite grains shows no zoning and relatively low u and th concentrations stark contrasts are visible between the ore depleted mantle influence and host rocks crustal influence in the whole rock lu hf and sm nd data the depleted mantle signature of the ore could be related to the kiruna greenstone group as a potential source region for the iron the sm nd isotopic composition of monazite from the ore shows a crustal influence and indicates that the younger event has not disturbed the whole rock sm nd signature of the ore the hydrothermal nature of the ore zircon grains and the isotopic signatures point to a hydrothermal influence on the ore formation with a high temperature magmatic fluid related to the intrusions as most likely heat and fluid source

rapid cooling and exhumation in the western part of the mesoproterozoic albany fraser orogen western australia abstract the albany fraser orogen of southwestern australia is an understudied orogenic belt which is interpreted to record the mesoproterozoic suturing of the yilgarn craton of western australia to the mawson craton of east antarctica during rodinia assembly previous u pb geochronology has dated peak amphibolite to granulite facies metamorphism in the orogen at ca 1180 ma here we report the first 40ar 39ar thermochronology of hornblende biotite and muscovite grains from a 360 km transect across the western albany fraser orogen and uncover a record of strikingly fast syn orogenic cooling and exhumation to the north muscovites from the northern foreland record cooling at ca 1159 ma in the central and southern domains of the orogen the biranup and nornalup zones hornblende yields ca 1169 ma cooling ages and biotite yields ca 1172 1144 ma cooling ages the new cooling ages imply that the three domains were exhumed rapidly following peak metamorphism at ca 1180 ma attained a similar structural level by ca 1159 ma and have experienced a uniform exhumation history since that time to constrain mineral closure temperatures and post peak metamorphic cooling rates we conducted a monte carlo simulation which fully propagates uncertainty and minimises error correlations modelling of cooling from hornblende to biotite closure temperatures ca 585 c and 365 c respectively in the nornalup and biranup zones yields fast cooling rates of 33 9 17 c ma and 22 5 7 c ma respectively these fast cooling rates imply rapid exhumation in an active tectonic setting undergoing peak metamorphism although the structural evolution of the albany fraser orogen remains poorly constrained the transpressional tectonic activity associated with deformation in the western part of the albany fraser orogen may have been an active driver of this fast exhumation this is distinctly different from exhumation models for granulite facies domains in other mesoproterozoic orogens which typically experience post orogenic slow 1 5 c ma cooling driven by mechanisms such as orogenic collapse and erosion we consider that the observed differences reflect the interpreted syn tectonic transpressional exhumation history of the albany fraser orogen which is an underrepresented tectonic regime in the mesoproterozoic cooling record

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

direct evidence for a steep geotherm under conditions of rapid denudation western himalaya pakistan recent fluid inclusion and 40 ar 39 ar cooling age data show that currently exposed basement rocks in the raikhot glacier valley of the nanga parbat haramosh massif pakistan himalaya were at temperatures of 350 50 c at depths of 6 2 km hydrostatic pressure correction these data imply the presence of a steep thermal gradient in the upper crust at 1 ma 29 100 c km and denudation rates over the past 1 0 m y of 3 6 mm yr providing independent corroboration of previous estimates of rapid denudation at nanga parbat 4 5 mm yr over 3 3 m y our data provide direct documentation of near surface compaction of isotherms under conditions of rapid denudation a result that has long been supported by thermal modeling

mafic sheets from indian plate gneisses in the nanga parbat syntaxis their significance in dating crustal growth and metamorphic and deformation events

tectono thermal evolution of the palaeoproterozoic granites tanami orogen north australian craton implications from hornblende and biotite 40ar 39ar geochronology abstract the palaeoproterozoic granites tanami orogen gto hosts a number of gold deposits located in the southern margin of the north australian craton the major stratigraphic succession is the palaeoproterozoic tanami group which is subdivided into the dead bullock formation and conformably overlying killi killi formation new geochemical data for the ca 1864 coora and groundrush dolerite sills in the dead bullock formation suggests that they have the same characteristics with the enriched back arc basin basaltic rocks from the former stubbins formation such as tholeiitic affinity high tio 2 contents 0 94 to 1 24 wt and low mg 41 45 slightly enriched lile rb th u and k weakly depleted hfse nb ta and relatively flat ree patterns their magma was generated by high degree decompressional melting 5 15 of the asthenosphere source with an input of 3 4 subduction related material the petrological and geochemical similarities of igneous rocks provide new evidence for the assignment of the ca 1864 ma former stubbins formation and the mount charles formations in the dead bullock formation of the tanami group these conclusions confirmed that the extensive palaeoproterozoic tanami group was deposited in a back arc basin environment hornblende and biotite 40 ar 39 ar geochronological study identified three major tectono thermal events in the gto since the deposition of the dead bullock formation the ca 1840 ma 40 ar 39 ar cooling age of metamorphic hornblende from the coora and groundrush dolerite sills in the dead bullock formation provided precise age constraint for the first palaeoproterozoic tectono thermal event during the evolution of the granites tanami back arc basin this age is highly consistent with the ca 1850 1840 ma subduction and peak metamorphism events in the north australian craton nac associated with the halls creek orogeny in the halls creek orogen and the tennant orogeny in the tennant creek inlier the 40 ar 39 ar age of 1753 8 ma for the early biotite bi b from the dead bullock formation is a cooling age record of the peak greenschist facies metamorphism during the ca 1795 ma tanami orogeny which is interpreted as the continental continental collisional event between the gto and the arunta orogen in the central australian craton to the south the approximately 40 million year slow cooling is a combined result of exhumation heat released from the upwelling asthenospheric mantle regional magmatism and long term crustal residence this tectono thermal event was associated with gold mineralisation in the gto and the proterozoic nac was finally cratonised during this period the late biotite bi g is a recrystallization product of hydrothermal alteration its 40 ar 39 ar age of 1718 8 ma revealed the last tectono thermal overprint to the gto and arunta orogen this age reflected the distal thermal influence by the ca 1723 ma strangways event in the arunta orogen

clockwise p t paths for crustal melting and h2o recycling in granite source regions and migmatite terrains abstract clockwise pressure temperature p t paths of metamorphism pass through two kinds of melting reactions with increasing temperature the first generates h 2 o saturated partial melts at the h 2 o saturated solidus only if excess h 2 o is present usually this accounts for less than 3 melt the second generates h 2 o undersaturated melts through dehydration melting reactions dmrs of micas or other hydrous minerals and occurs at temperatures higher than the h 2 o saturated solidus if h 2 o undersaturated melts remain in situ and the source regions are not exhumed then the crystallisation reactions encountered along the near reverse p t path may produce the same mineralogy as in the source rock in regions of exhumation along the decompression segments of clockwise p t paths two other types of crystallisation reactions occur the better known type occurs at the recrossing of the pelite h 2 o saturated solidus at shallower depth this can occur at mid crustal depths or much shallower at pressures lower than the appropriate invariant point which relates all of these reactions and will result in granitic pegmatites at the other type remaining mica can react with hydrous melt to generate anhydrous granulite with free h 2 o fluid such suprasolidus decompression dehydration reactions sddrs result in freezing of pelitic melts at mid crustal depth to k feldspar quartz assemblages and release of h 2 o which can induce h 2 o saturated melting in adjacent fertile lithologies lacking h 2 o e g psammite older granite distinct mineral proportions and textures will result from each reaction the actual reactions occurring are related through specific invariant points whose locations are known in the p t space the displacement of these invariant points due to additional components in the solid melt and fluid phases is reasonably well known the flat lying sddr very low d p d t will extend to much higher pressures if a low ah 2 o fluid is present sddr involving amphibole or epidote will occur in mafic to intermediate compositions over a large depth range depending on fe mg ca na etc of the rock compositions

anatomy of a continental subduction zone the main mantle thrust in northern pakistan the himalayas form an ideal natural laboratory to study the deformation processes of continental crust during collision orogeny new information is presented concerning the structural evolution of the main mantle thrust zone in the himalayas of n pakistan in the region around nanga parbat the hanging wall lies at relatively high levels within the kohistan arc terrane which has been emplaced onto indian continental rocks this thrust probably originated as a breakback structure in the hanging wall to the pre collisional oceanic subduction zone the present hanging wall contains a shear zone of about 1 km width developed under amphibolite facies conditions simple shear dominant strains have developed new fabrics parallel to the main thrust zone however these structures are redeformed by discrete extensional and compressional shears within about 100 m of the thrust contact again developed under amphibolite facies conditions the footwall consists of an old basement complex the nanga parbat gneisses overlain by a distinct suite of metasediments now at amphibolite facies this cover assemblage of psammites pelites and marbles with local metabasites consistently lies directly against rocks derived from the kohistan arc along the mmt the absence of structures suggestive of consistent rheological contrasts within the cover assemblages suggests that the vast majority of the deformation features they contain were developed only once they experienced substantial tectonic overburdens prior to this the indian cover rocks will have been passively subducted beneath the kohistan arc until into amphibolite facies we discuss these inferences in terms of evolving shear zone width with time and comment on the implications for predicting the character of mid deep crustal shear zones particularly from seismic reflection profiles

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

modelling storm hydrodynamics on gravel beaches with xbeach g abstract in this paper we present a process based numerical model for the prediction of storm hydrodynamics and hydrology on gravel beaches the model comprises an extension of an existing open source storm impact model for sandy coasts xbeach through the application of 1 a non hydrostatic pressure correction term that allows wave by wave modelling of the surface elevation and depth averaged flow and 2 a groundwater model that allows infiltration and exfiltration through the permeable gravel bed to be simulated and is referred to as xbeach g although the model contains validated sediment transport relations for sandy environments transport relations for gravel in the model are currently under development and unvalidated consequently all simulations in this paper are carried out without morphodynamic feedback modelled hydrodynamics are validated using data collected during a large scale physical model experiment and detailed in situ field data collected at loe bar cornwall uk as well as remote sensed data collected at four gravel beach locations along the uk coast during the 2012 2013 storm season validation results show that the model has good skill in predicting wave transformation overall sci 0 14 0 21 run up levels sci

isotope systematics of the kiruna magnetite ores sweden part 2 evidence for a secondary event 400 m y after ore formation the kiirunavaara magnetite apatite ore occurs within and is coeval with an acid 1 89 ga volcanic complex the whole overlying the kiruna greenstones the ore experienced an intensive hydrothermal event at around 1 5 ga some 400 m y after ore formation this event caused resetting of the sm nd isotope system in the magnetite ore itself but did not widely affect host rock sm nd systems the ore gives an sm nd isochron age of 1 49 or 0 13 ga mswd 2 1 in contrast the host rock sm nd systems are not reset but give an age consistent with u pb zircon ages the initial nd isotope composition epsilon 11 1 of the ore demonstrates that the rare earths in the ore had a long crustal residence and could not have been derived from the underlying kiruna greenstones it is similar to the intrusive igneous host rocks and a cogenetic origin is likely whole rock rb sr and u pb systems are reset in both the ore and host rocks resetting of the former system is observed on a regional scale throughout northern sweden the only nonisotopic trace of the 1 5 ga event in the ore is the abundance of disseminated and vein pyrite or calcite or chalcopyrite which is locally concentrated in the primary magnetite apatite ore particularly along faults the lead isotope compositions of these pyrites are similar to lead isotope compositions from ore and host rocks they all plot on a secondary isochron with an age of 1 54 or 0 07 ga mswd 2 39 the porous textures of the magmatic magnetite primary ore as well as the faults may both have enhanced penetration of hydrothermal fluids thereby localizing more intensive resetting the evidence suggests that the late stage pyrite chalcopyrite mineralization in the kiruna ores is not part of the primary magnetite paragenesis but was imposed upon the deposit at a later stage the sulfide paragenesis appears to reflect a low temperature hydrothermal event related to regional uplift and associated alteration of host rocks extension of kiruna type magnetite apatite ores to embrace iron and copper sulfide facies may be misleading

erosion and exhumation in the himalaya from cosmogenic isotope inventories of river sediments the outward erosional flux is a key factor in the tectonic evolution of mountain belts and there is much debate about the feedbacks between tectonics erosion and climate here we use cosmogenic nuclides 10be and 26al analysed in quartz from river sediments from the upper ganges catchment to make the first direct measurements of large scale erosion rates in a rapidly uplifting mountain belt the erosion rates are highest in the high himalaya at 2 7 0 3 mm yr 1 errors fall to 1 2 0 1 mm yr on the southern edge of the tibetan plateau and are 0 8 0 3 to 0 6 mm yr in the foothills to the south of the high mountains these relative estimates are corroborated by the nd isotopic mass balance of the river sediment analysis of sediment from an abandoned terrace suggests that similar erosion rates have been maintained for at least the last few thousand years the data presented here along with data recently published for european river catchments demonstrate that a log linear relationship between relief and erosion rate holds over three orders of magnitude variation in erosion rate and between very different climatic and tectonic regimes the erosion rate estimates from cosmogenic nuclides correlate well with exhumation rates calculated from previously published apatite fission track ages in the indian himalaya this confirms that much of the exhumation in the himalayan mountain chain is now balanced by erosion however exhumation rates calculated from high blocking temperature systems such as 40ar 39ar in muscovite imply lower exhumation rates rocks presently at the surface must have undergone a three to six fold increase in exhumation rate within the last few million years we show how this could be explained either by climatic forcing of erosion rate changes or by tectonics published evidence for equally rapid changes of exhumation rate in the past and the probable diachroneity in the time at which the present exhumation rates accelerated imply that tectonics has moderated at least some of the change in exhumation rates

new constraints on the timing of host rock emplacement hydrothermal alteration and iron oxide apatite mineralization in the kiruna district norrbotten sweden high spatial resolution zircon u pb geochronological data obtained directly on the kiirunavaara iron oxide apatite ioa deposit related orebodies and host rocks provide new constraints on the timing of mineralization in these deposits these data raise new arguments in the debate of a magmatic versus hydrothermal metasomatic genesis of these major 2 500 mt 30 70 wt fe paleoproterozoic deposits the main orebody at kiirunavaara contains ti poor magnetite and minor 0 05 5 wt p apatite located between a trachyandesite footwall and a rhyodacite hanging wall which also hosts smaller orebodies nukutus rektorn and tuolluvaara the pervasive na and k metasomatism in the host rock is documented by whole rock geochemical data and cathodoluminescence cl microscopy zircon u pb data for the metavolcanic rocks in the footwall and hanging wall cluster between 1884 4 and 1880 3 ma in the footwall a syenite aplite system yields ages of 1880 7 and 1881 4 ma a granite pluton exposed underground has an age of 1874 4 ma zircons in two ore samples never directly dated before this study yield ages of 1877 4 and 1874 7 ma brecciation at the contacts between the ore and host rocks the tight age at ca 1880 ma for most volcanic and plutonic rocks in the footwall and hanging wall and the marginally younger age for ore at ca 1877 to 74 ma matching the age of the spatially related granite pluton suggest a magmatic hydrothermal emplacement model for the kiruna area ioa ores

improved confidence in u th he thermochronology using the laser microprobe an example from a pleistocene leucogranite nanga parbat pakistan 1 the newly developed laser microprobe u th he thermochronometer permits for the first time the ability to generate precise u th he cooling ages for even very young 1 ma samples with a spatial resolution on the order of tens of micrometers this makes it possible to test the reproducibility of independent u th he age determinations within individual crystals further increasing the reliability of the method as an example we apply it here to a pleistocene granite from nanga parbat pakistan where previous constraints on the thermal history are consistent with rapid exhumation and cooling twenty one u th he dates determined on two monazite crystals from a single granite sample yield a mean of 748 000 years with a 95 confidence level of 19 000 years there is no discernible variation in the distribution of u th he ages in the cores of these crystals and therefore no evidence for the development of substantial diffusive loss 4he zoning over 80 of the interior of the monazite crystals during postcrystallization cooling of the granite modeling of these data suggests that cooling at a mean rate of 300 k ma would be necessary to produce the observed ages and the lack of a 4he gradient which is consistent with preexisting constraints for nanga parbat increased precision in thermochronology permits more tightly constrained exhumation models which should aid geologic interpretation

in situ u pb and trace element analysis of accessory minerals in the kiruna district norrbotten sweden new constraints on the timing and origin of mineralization northern norrbotten sweden is a key part of baltic shield and provides a record of magmatic tectonic and related superimposed fe oxide apatite and iron oxide copper gold iocg mineralization during the svecokarelian orogeny titanite and allanite from a range of mineral deposits in the area have been analysed for u pb isotope systematics and trace element chemistry using laser ablation quadrupole inductively coupled plasma mass spectrometry la icp ms analyses of a single sample from the regional scapolite albite alteration give an age of 1903 8 ma 2 and may be contemporaneous with the early stages of fe mineralization 1890 1870 ma analyses of titanite and allanite from undeformed iocg deposits indicate initial alteration at 1862 16 ma in many deposits subsequent metamorphic effects reset titanite isotope systematics from 1790 to 1800 ma resulting in a spread of u pb isotope analyses along concordia in some instances core regions may record evidence of early thermal events at around 2050 ma titanite and allanite from deformed iocg deposits on major shear zones record ages from 1785 21 ma to 1777 20 ma corresponding to deformation metamorphism and secondary hydrothermal alteration as a result of late orogenic movements the lack of intracrystalline variations in titanite and allanite trace element chemistry suggests that hydrothermal fluid chemistry and metal source were the main controls on mineral trace element chemistry titanite from undeformed fe oxide apatite and iocg deposits is typically light rare earth element lree enriched and shows low u th ratios and low ni in both intermediate to acid and basic volcanic hosted deposits this is consistent with a granitic source for metals minor variations in trace element patterns are consistent with the influence of aqueous complex formation on relative ree solubility deposits related to the nautanen deformation zone have relatively heavy ree hree enriched titanite and lree depleted allanite with high u th ratios and elevated ni contents consistent with leaching of metals from the local basic volcanic rocks all hydrothermal titanites are high field strength element enriched nb ta zr indicating their transport as a result of either high salinities or high f contents or both the data overall support models of iocg type mineralization as a result of regional circulation of saline hydrothermal fluids in association with major crustal structures with at least some metallic components derived from the granitoid rocks of the area all the deposits here show evidence of subsequent metamorphism although penetrative fabrics are restricted to regional scale deformation zones

mazeno pass pluton and jutial pluton pakistan himalaya age and implications for entrapment mechanisms of two granites in the himalaya zircon and monazite u th pb ion microprobe analysis were performed on the mazeno pass pluton and the jutial pluton two leucogranite bodies within the nanga parbat haramosh massif nphm pakistan himalaya zircon rim ages and monazite ages indicate the mazeno pass pluton in southwest nphm intruded at 1 40 0 05 ma the jutial pluton to the north similarly yields concordant zircon and monazite ages suggesting crystallization at 9 45 0 06 ma the jutial pluton was subsequently intruded by leucogranite dikes at 5 3 ma as revealed by monazite ages concordancy of u pb and th pb accessory mineral ages demonstrates the robustness of the technique on young rocks both plutons some of the youngest in the himalaya have a general association with nearby shear zones that we interpret to have played an integral role in granite evolution and emplacement setting deformation enhanced ascent together with new field observations these results provide an insight on the spatial and temporal relationship between plutonism and deformation relating to the development of the massif

constraints on unroofing rates in the high himalaya eastern nepal thermobarometric data for samples across the main central thrust zone in eastern nepal show an inversion in temperature but not in pressure these data have been interpreted to represent a portion of the paleogeotherm at the time of main central thrust deformation a 40ar 39ar age on hornblende closure temperature tc 500 50 c constrains the timing of this deformation to be 21 0 2 ma the 40ar 39ar ages of other minerals muscovite tc 350 c age t 12 0 0 2 ma k feldspar tc 220 c t 8 0 0 2 ma from the same location further constrain the cooling history of this region together the geochronologic and thermobarometric data yield an average unroofing rate of 1 2 0 6 mm yr for the high himalaya of eastern nepal simple thermal models show that these geochronologic and thermobarometric data are consistent with a wide range of different initial geotherms applied boundary conditions and magnitude of radiogenic heat production the variation through time of the unroofing rates can only be poorly constrained however the unroofing histories were found to be largely insensitive to the details of the assumed initial geotherm fairly sensitive to the magnitude of radiogenic heat production and extremely sensitive to the nature of the boundary conditions applied below the fault zone this study underscores the difficulty in constraining uplift histories on the basis of cooling rates even when thermobarometric data are available to supplement geochronologic constraints on the cooling history of the region

asynchronous formation of the adjacent epithermal au cu and porphyry cu mo deposits in the zijinshan orefield southeast china abstract adjacent high sulfidation epithermal hse and porphyry deposits often have similar cu au metal association suggesting they are cogenetic and formed contemporaneously the zijinshan orefield zof is the largest au producer in china and contains a series of hse au cu and porphyry cu mo deposits this study presents new 1 muscovite 40ar 39ar ages for the hse deposit in this area new 2 zircon laser ablation inductively coupled plasma mass spectrometry la icp ms u pb ages for felsic igneous rocks associated with the epithermal and porphyry mineralization and 3 new zircon lu hf isotopic data for these intrusions all of which provides insights into why these adjacent epithermal au cu and porphyry cu mo deposits have different metal associations the age data indicate that the alunite dickite alteration related to the hse au cu mineralization formed before ca 110 ma and the main hse au cu mineralizing event occurred at ca 113 ma in comparison the adjacent porphyry cu mo mineralization formed at ca 104 ma ca 9 myr after the hse event the volcanic rocks associated with the hse au cu mineralization yield zircon ehf t values from 4 1 to 0 3 whereas the cu mo mineralized porphyry has lower zircon ehf t values 4 5 to 1 2 suggesting that the magmas that formed the latter intrusion were derived from a source containing more crustal material than the magmas associated with the hse mineralization the differences in the timing of mineralization and the sources of the magmas indicate that the adjacent hse and porphyry deposits in the zof formed from different magmatic hydrothermal systems that controlled the different metal associations of the mineralizing systems this means that future mineral exploration within the zof should target porphyry au cu deposit at depths that is genetically related to the hse au cu deposit the results also show that not all adjacent porphyry and epithermal deposits especially those with different metal associations are cogenetic

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

insights into the patterns and locations of erosion in the himalaya a combined fission track and in situ sm nd isotopic study of detrital apatite understanding the role that climate erosion and tectonics play in determining the mean relief elevation and general form of a mountain range over time has become the focus of much recent research in the field of tectonic geomorphology a crucial constraint in these studies is the long term exhumation rate which is increasingly being examined using detrital minerals from the sedimentary rock record that represent the eroded remnants of the orogen a classic field area of such studies is the himalayan orogen the earth s largest mountain range we describe here a novel approach that uses the in situ analysis of nd isotopes by laser ablation multicollector inductively coupled plasma mass spectrometry of fission track dated apatite grains to unambiguously tie them to their source regions we demonstrate the capability of this new approach on several modern and holocene river sand samples from the himalayan orogen and determine because of the large isotopic differences in the constituent tectonostratigraphic units both the location and magnitude of long term erosion in agreement with previous studies we are able to show that in the central and eastern himalaya long term denudation is focussed within the high himalayan crystalline series hhcs at average rates of not vert similar 2 mm yr average long term rates are similar in the western himalaya sampled by the indus river and largely reflect erosional denudation of the western indian himalaya and the western syntaxis the nanga parbat haramosh massif and south karakoram metamorphic complex notably the asian continent supplies significantly more apatites to the mouth of the indus than they do to the bengal delta the ability to reconstruct the patterns of long term erosion in the himalaya using detrital apatites from a few samples collected from major transverse drainages provides confidence in the utility of this approach to examine the locations and magnitude of long term erosion in the past

spatially variable exhumation rates in orogenic belts an andean example abstract the cordillera real of the bolivian andes is a large tectonically active mountain range that dominates sediment influx into the amazon basin but rates of exhumation in the orogen are poorly known we present 20 new apatite fission track ages from two valleys in the cordillera real to constrain patterns of mountain range exhumation over 106 107 yr we interpret these and previously published data from a third valley using a 2 d thermal model that accounts for topographic and advective influences on measured cooling ages exhumation rates in the cordillera real are 0 2 0 6 mm yr comparable to rates in parts of denali the washington cascades the olympic mountains and the european alps and an order of magnitude slower than rates in taiwan nanga parbat the greater himalaya of nepal and the southern alps of new zealand three to fourfold cooling age variations in the cordillera real imply at least twofold exhumation rate variations within and between valleys over distances of only tens of ki

exhumation overrated at nanga parbat northern pakistan abstract new 40 ar 39 ar laserprobe and thermobarometric data from the nanga parbat haramosh massif nphm in northern pakistan provide important constraints on thermal models of the evolving geotherm of the massif simple thermal models indicate that the unusually young cooling ages from this area do not necessarily imply extreme exhumation rates of about 7 mm y because the advection of heat resulting from rapid exhumation leads to a steepened near surface geotherm the most important control on the present day thermal structure of the nphm appears to be the thermal structure resulting from obduction of the kohistan arc some 50 m y ago transient geotherms calculated for the past 10 ma can only be reconciled with published geochronological and thermobarometric studies if exhumation rates lay in the range of 3 to 4 mm y still considerably greater than exhumation rates determined from the main himalayan orogen

numerical modelling of the thermal history of the nw himalayas kullu valley india abstract this paper demonstrates two dimensional time dependent finite difference modelling of himalayan metamorphism illustrated by the kullu s lahul area himachal pradesh after the collision between india and asia and the over thrusting of the higher himalayas over the lesser himalayas it is shown that a one dimensional model with crustal thickening by a single thrust cannot satisfy the observations present in the section along the kullu valley a two dimensional solution demonstrates that during thrust sheet emplacement at geologically realistic strain rates of several centimetres a year a temperature inversion does not occur in contrast to the inversion assumed by the one dimensional instantaneous thrust models therefore the variability of two other model parameters were explicitly considered i there is a significant conductivity contrast between the different types of rocks as conductivity layers function as a barrier to the transport of heat the conductivity limit should be variable for different regions in the grid ii rocks in the higher himalayas record a phase of metamorphism that preceded the movements on the main central thrust this observation together with the knowledge that rocks with different radiogenic heat production and conductivity are not uniformly distributed in the crust emphasizes that there were considerable horizontal temperature variations across the whole region for that reason the initial temperature profile too has to be adapted for a realistic model

beach morphodynamics and types of foredune erosion generated by storms along the emilia romagna coastline italy abstract the objectives of this study are to examine the response of a dune and beach system on the adriatic coastline in northern italy to the arrival of storms compare it with seasonal months and medium term 3 year morphodynamic change and evaluate results predicted by the numerical model xbeach the studied coastline stretches 4 km from the bevano river mouth to the north of the site to the township of lido di classe to the south where the beach is protected by coastal structures fieldwork consisted of topographic profile surveys using rtk dgps technology 7 times over an approx 3 year period 103 samples of surface sediment were collected along 20 of the cross shore profiles at 6 distinct cross shore positions selected on the basis of morphological beach characteristics data analyses of dune and beach slopes enabled the study area to be divided into 6 separate morphological zones using the spatial longshore and cross shore variation of morphologies located on the backshore and intertidal beach observed in a preliminary survey of the area other criteria were a spatial consistency in beach slopes and or presence absence of intertidal morphologies identified in the aerial photographs and lidar data the swash zone slope did not show any significant variability for the entire area a weak seasonal trend in the variability of the mean foredune slope was observed with steeper slopes typically during winter and flatter slopes during summer analysis of grain size revealed that the beach sediment is well sorted fine sand tending to medium with a decreasing trend in size from the bevano river mouth southwards towards lido di classe according to the masselink and short 1993 classification the natural part of the study site has an intermediate barred beach ibb and following the short 1999 classification results in a modally lbt longshore bar trough or ltt low tide terrace with a small section being tbr transverse bar and rip storms are considered the main factor controlling changes in the beach and dune slope the most significant storm was recorded in march 2010 with a peak significant wave height of 3 91 m contrary to the seasonal dune trend several foredune slopes were observed to flatten following this event which can be attributed to the action of dune slumping from the already weakened dune state modelling of foredune erosion using a process based model xbeach reproduced the erosion of the upper beach and dune toe reasonably well but is currently limited by the acceptable slope value for dune stability which does not account for biotic factors e g plant roots the comparison between the storm impact categories of sallenger 2000 and the dsf dune stability factor of armaroli et al 2012 shows a very good correspondence between the effects of the winter 2008 2009 storms and the vulnerability of the dune system predicted using both classifications

new insight into the dynamic development of the southern alps new zealand from detailed thermochronological investigation of the mataketake range pegmatites

the pilot knob magnetite deposit in the proterozoic st francois mountains terrane southeast missouri usa a magmatic and hydrothermal replacement iron deposit abstract the pilot knob magnetite deposit is located in southeast missouri within the 1380 1480 ma st francois mountains terrane rhyolitic trachytic volcanic rocks the deposit is tabular dips about 45 and is sill like in nature being approximately parallel to the bedding in the host tuffs the deposit was uncovered by erosion and exposed to weathering in the late proterozoic and is overlain in angular unconformity by the cambrian lamotte sandstone this proterozoic weathering cycle apparently had little effect on the deposit with only the updip edge being converted to hematite textural and mineralogical features of the deposit suggest a combined magmatic and hydrothermal replacement origin the magnetite rich ores that make up the bulk of the deposit are interpreted as having crystallized from an iron rich magma and a surrounding envelope of lower to moderate grade ores where magnetite has clearly replaced the tuffaceous host rocks are interpreted as hydrothermal in origin after the development of the higher grade magnetite ores and the envelope of lower to moderate grade ores late hydrothermal minerals were deposited as cross cutting veins and breccia fill the two most abundant minerals in the higher grade portions of the deposit are magnetite and albitic plagioclase and petrologically the higher grade ores could be described as a magnetite sodic syenite the most abundant gangue mineral within the lower grade impregnated envelope of ores around the higher grade ores is k feldspar apparently relict from the rhyolites trachytes thin lenses within the higher grade ores contain calcite as a matrix mineral to the magnetite and are considered to indicate carbonatitic affinity rare earth elements are elevated in one of five whole rock chemical analyses of the ores and the ree bearing mineral ferriallanite has been identified minor portions of the deposit below the proterozoic weathering cap consist of high grade hematite ores having equilibrium textures at depth the deposit is intruded by the shepherd mountain gabbro a 120 m thick near horizontal dike which resulted in minor contact metamorphism of the ore

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

feeding the aneurysm orogen parallel mass transport into nanga parbat and the western himalayan syntaxis the nanga parbat haramosh massif nphm western himalayan syntaxis requires an influx of mass exceeding that in the adjacent himalayan arc to sustain high topography and rapid erosional exhumation rates what supplies this mass flux and feeds this tectonic aneurysm we show using a simple 3 d model of oblique orogen convergence that velocity strain partitioning results in horizontal orogen parallel op crustal transport and the same behavior is inferred for the himalaya with op transport diverting converging crust toward the syntaxis model results also show that the op flow rate decreases in the syntaxis thereby thickening the crust and forming a structure like the nphm the additional crustal thickening over and above that elsewhere in the himalayan arc sustains the rapid exhumation of this aneurysm normally velocity strain partitioning would be minimal for the himalayan arc where the convergence obliquity is no greater than 40 however we show analytically that the himalayan system can act both as a critical wedge and exhibit strain partitioning if both the detachment beneath the wedge and the bounding rear shear zone which accommodates op transport are very weak corresponding numerical results confirm this requirement and demonstrate that a nanga parbat type shortening structure can develop spontaneously if the orogenic wedge and bounding rear shear zone can strain rate soften while active these results lead us to question whether the position of nphm aneurysm is localized by river incision as previously suggested or by a priori focused tectonic shortening of the crust in the syntaxis region as demonstrated by our models

evaluation of wave runup predictions from numerical and parametric models abstract wave runup during storms is a primary driver of coastal evolution including shoreline and dune erosion and barrier island overwash runup and its components setup and swash can be predicted from a parameterized model that was developed by comparing runup observations to offshore wave height wave period and local beach slope because observations during extreme storms are often unavailable a numerical model is used to simulate the storm driven runup to compare to the parameterized model and then develop an approach to improve the accuracy of the parameterization numerically simulated and parameterized runup were compared to observations to evaluate model accuracies the analysis demonstrated that setup was accurately predicted by both the parameterized model and numerical simulations infragravity swash heights were most accurately predicted by the parameterized model the numerical model suffered from bias and gain errors that depended on whether a one dimensional or two dimensional spatial domain was used nonetheless all of the predictions were significantly correlated to the observations implying that the systematic errors can be corrected the numerical simulations did not resolve the incident band swash motions as expected and the parameterized model performed best at predicting incident band swash heights an assimilated prediction using a weighted average of the parameterized model and the numerical simulations resulted in a reduction in prediction error variance finally the numerical simulations were extended to include storm conditions that have not been previously observed these results indicated that the parameterized predictions of setup may need modification for extreme conditions numerical simulations can be used to extend the validity of the parameterized predictions of infragravity swash and numerical simulations systematically underpredict incident swash which is relatively unimportant under extreme conditions

petrology of indus river sands a key to interpret erosion history of the western himalayan syntaxis the indus river has been progressively transformed in the last decades into a tightly regulated system of dams and channels to produce food and energy for the rapidly growing population of pakistan nevertheless indus river sands as far as the delta largely retain their distinct feldspar and amphibole rich composition which is unique with respect to all other major rivers draining the alpine himalayan belt except for the brahmaputra both the indus and brahmaputra rivers flow for half of their course along the india asia suture zone and receive major contributions from both asian active margin batholiths and upper amphibolite facies domes rapidly exhumed at the western and eastern himalayan syntaxes compositionofindussandschangesrepeatedlyandmarkedlyinladakhandbaltistan indicatingoverwhelmingsedimentflux from each successive tributary as the syntaxis is approached provenance estimates based on our integrated petrographic mineralogical data set indicate that active margin units karakorum and transhimalayan arcs provide 81 of the 250f50 10 6 t ofsedimentsreachingthetarbelareservoireachyear partitioningofsuchfluxamongtributariesandamongsourceunitsallowsus to tentatively assess sediment yields from major subcatchments extreme yields and erosion rates are calculated for both the karakorum belt up to 12 500f4700 t km 2 year and 4 5f1 7 mm year for the braldu catchment and nanga parbat massif 8100f3500t km 2 yearand3 0f1 3mm year thesevaluesapproachdenudationratescurrentlyestimatedforsouthkarakorum and nanga parbat crustal scale antiforms and highlight the major influence that rapid tectonic uplift and focused glacial and fluvial erosion of young metamorphic massifs around the western himalayan syntaxis have on sediment budgets of the indus system detailed information on bulk petrography and heavy minerals of modern indus sands not only represents an effective independent method to constrain denudation rates obtained from temperature time histories of exposed bedrock but also

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

synchronous anatexis metamorphism and rapid denudation at nanga parbat pakistan himalaya the nanga parbat haramosh massif of the western himalaya is a north trending half window of indian crust that provides spectacular exposures of precambrian basement gneisses that have been overprinted by himalayan metamorphism we report here petrologic data and u pb dates on zircon and monazite which document that nanga parbat gneisses underwent a pliocene pleistocene episode of high grade metamorphism and anatexis during an interval in which the nanga parbat massif was undergoing rapid denudation at mean rates of 5 mm yr we speculate that by initiating decompression melting this denudation may be at least partly responsible for the anatexis and high grade metamorphism

cooling and exhumation history of the northeastern gawler craton south australia abstract we present biotite 40ar 39ar ages and from the palaeo to mesoproterozoic mount woods inlier in the northeastern gawler craton south australia in combination with garnet biotite fe mg exchange modelling using the thermal history program these data are used to constrain a post peak metamorphic p t path cooling rates and a temperature time path for the inlier consistently well defined plateaus at 1 53 ga of biotite 40ar 39ar age spectra indicate that the rocks cooled through 300 c at this time cooling rates within the inlier are 3 9 c ma from peak high temperature low pressure metamorphism at 1 59 ga to 1 53 ga cooling rates subsequently decreased to 4 c ma cooling is suggested to be a function of cessation of voluminous magmatism and mantle heat input in conjunction with exhumation initiated along the southwestern margin of the inlier ca 1 592 1 582 ga the temperature time path of the inlier has a concave shape the peak metamorphic and ensuing cooling history of the mount woods inlier are akin to the nearby curnamona province coober pedy ridge and mabel creek ridge within the south australian craton deformation during high grade metamorphism within these terranes was accommodated at mid crustal levels and large scale exhumation did not occur until the terranes cooled and were able to be exhumed as coherent rigid blocks along discrete shear zones and faults

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

marano volcanic rocks east azarbaijan province iran and associated fe mineralisation there are two main types of economic iron ore deposits in iran 1 magmatic segregation deposits and 2 skarns most of the hydrothermal iron deposits in iran except for the skarns are uneconomic one of these uneconomic hydrothermal deposits is the marano fe deposit located in east azarbaijan province nw iran this deposit is considered to have been formed by an epithermal style of mineralisation related to a volcanic dome there are 5 volcanic domes in the marano area ranging in composition from dacite to rhyolite the volcanic rocks show geochemical evidence of fractionation of biotite hornblende magnetite apatite and feldspars the marano volcanic domes crystallised from an i type magma formed in a volcanic arc setting fe mineralisation has occurred around one of these marano domes ma dome in which the igneous rocks contain more biotite and hornblende and are less fractionated than in the other domes the main fe oxide hematite occurs as veins and disseminations in sedimentary wall rocks alteration of the minerals in the host rocks suggests a s 2 9 5 a o 2 10 34 2 and ph 5 5 the small size and shallow level of emplacement of magma together with the absence of extensive hydrothermally altered zones shows that the hydrothermal system was not voluminous enough to form an economic iron deposit

the sources and evolution of mineralising fluids in iron oxide copper gold systems norrbotten sweden constraints from br cl ratios and stable cl isotopes of fluid inclusion leachates we have analysed the halogen concentrations and chlorine stable isotope composition of fluid inclusion leachates from three spatially associated fe oxide cu au mineralising systems in norrbotten sweden fluid inclusions in late stage veins in fe oxide apatite deposits contain saline brines and have a wide range of br cl molar ratios from 0 2 to 1 1 10 3 and 37cl values from 3 1 to 1 0 leachates from saline fluid inclusions from the greenstone and porphyry hosted cu au prospects have br cl ratios that range from 0 2 to 0 5 10 3 and 37cl values from 5 6 to 1 3 finally the cu au deposits hosted by the nautanen deformation zone ndz have br cl molar ratios from 0 4 to 1 1 10 3 and 37cl values that range from 2 4 to 0 5 although the bulk of the data fall within 0 0 5 the br cl ratios of leachates are consistent with the derivation of salinity from magmatic sources or from the dissolution of halite most of the isotopic data from the fe oxide apatite and greenstone deposits are consistent with a mantle derived source of the chlorine with the exception of the four samples with the most negative values the origin of the low 37cl values in these samples is unknown but we suggest that there may have been some modification of the cl isotope signature due to fractionation between the mineralising fluids and cl rich silicate assemblages found in the alteration haloes around the deposits if such a process has occurred then a modified crustal source of the chlorine for all the samples cannot be ruled out although the amount of fractionation necessary to generate the low 37cl values would be significantly larger the source of cl in the ndz deposits has a crustal signature which suggests the cl in this system may be derived from meta evaporites or from input from crustal melts such as granitic pegmatites of the lina suite