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

retrogression by deep infiltration of meteoric fluids into thrust zones during late orogenic rapid unroofing hypersaline na ca cl fluids are associated with late stage quartz veining and retrogression of garnet kyanite and other high p t phases in the vicinity of thrusts and major lithological boundaries in the scandian nappes of the troms ofoten region northern norway they record early devonian fluid infiltration during rapid exhumation in the final stages of caledonian orogenesis the d18o and dd characteristics of these late fluids provide compelling evidence for deep circulation of meteoric fluids the sub greenschist to low greenschist facies retrogression p 2 1 kbar t 300 350 c suggests infiltration to depths of 7 9 km in a regime of supra hydrostatic fluid pressure peak metamorphic quartz veins and associated fluids have dd and d18o characteristics consistent with a metamorphic origin dd 47 to 75 d18o 8 6 to 17 4 however late quartz veins and associated fluids show a broad spread of dd from 42 to 148 interpreted in terms of meteoric fluid infiltration such negative dd values are only recorded in present day high latitude or high altitude settings and since north norway was in an equatorial setting 10 s in the early devonian a high altitude origin is deduced by calculation and by comparison with modern examples the early devonian mountains of the north norwegian caledonides are interpreted to have had a topography in excess of 5 km the deep circulation of surface waters is interpreted in terms of topographically driven flow linked with a hydrothermal system induced by elevated geothermal gradients due to rapid uplift whilst the case for deep penetration of surface derived fluids has been promoted for mesozoic and younger mountain belts this study represents one of the first documented examples for a palaeozoic orogenic belt it suggests that many of the fundamental processes operating during the exhumation of mountain belts are similar irrespective of age

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

grain boundary migration of water and carbon dioxide during uplift of garnet zone alpine schist new zealand deformed quartz veins in garnet zone schist adjacent to the active alpine fault new zealand have fluid inclusions trapped along quartz grain boundaries textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins many of the inclusions are empty but some contain carbon dioxide with densities that range from 0 16 to 0 80 g cm 3 no water nitrogen or methane was detected the inclusions are considerably more co2 rich than either the primary metamorphic fluid 5 co2 or fluids trapped in fracture related situations in the same or related rocks 50 co2 enrichment of co2 is inferred to have resulted from selective migration wicking of saline water from the inclusions along water wet grain boundaries after cooling induced immiscibility of a water co2 mixture inclusion volumes changed after loss of water non wetting co2 remained trapped in the inclusions until further percolation progressively removed co2 in solution this mechanism of fluid migration dominated in ductile quartz rich rocks near but below the brittle ductile transition at deeper levels hydraulic fracturing is also an important mechanism for fluid migration whereas at shallower levels advection through open fractures dominates the fluid flow regime

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

a geochemical model for fumaroles of the mutnovsky volcano kamchatka ussr abstract on the basis of the chemical isotopic and thermodynamic characteristics of fluids sampled between 1964 and 1989 a genetic model description is given for fumaroles of the mutnovsky volcano there are three individual groups of fumaroles in the mutnovsky crater which show stable activity for a long period of time the active funnel temperatures exceed 600 c the upper field up to 320 c and the bottom field from 100 to 150 c the three principal zones of emission have different gas composition water isotopic composition radioactivity and 3he 4he ratios the abundance of magmatic components in the high temperature fumaroles of the active funnel is much higher than those in gases from the other groups emission rate of so2 from the active funnel is about 200 t d which requires complete degassing as a minimum of 1 km3 of magma every 20 years fluids of the upper field contain up to 80 of steam from the mutnovsky geothermal system temperature variations of the bottom field fumaroles from 97 c before 1982 to 151 c in 1989 result from changes in hydrological conditions in the crater evaporation of high saline acid brine which is formed in the interior of the volcano is responsible for the composition of the bottom field gas steam discharges

incision and differential bedrock uplift along the indus river near nanga parbat pakistan himalaya from 10be and 26al exposure age dating of bedrock straths abstract well preserved river cut bedrock surfaces straths abandoned by the progressive incision of the indus river in northern pakistan were dated using in situ cosmogenic 10 be and 26 al exposure age dating measurements on young and modern straths show no significant ingrowth of 10 be and 26 al implying that strath exposure ages closely approximate their abandonment age strath exposure ages range up to 65 ka and increase with height above the river the straths can be divided into two groups low straths dated at about 7 ka which yield very rapid bedrock incision rates 9 12 m ka and high straths 7 ka in age which yield somewhat slower incision rates 1 6 m ka incision rates for both groups increase by 1 3 m ka downstream toward an active reverse fault the raikot fault that forms the western border of the nanga parbat haramosh massif nphm the downstream increases in incision rates for the low straths mimic downstream increases in the modern gradient suggesting that bedrock incision rates have been proportional to stream power over the last 7 ka gradient increases are probably the result of the creation of knickpoints by bedrock uplift along the raikot fault the longitudinal profile and steep gorge of the indus river in the study area indicate that bedrock incision appears to keep pace with differential vertical motions between the nphm and surrounding regions thus the 1 3 m ka difference in incision rates likely reflects the differential bedrock uplift rate between the nphm and the skardu basin the differential incision rate is consistent with differential exhumation rates obtained from apatite fission track ages assuming geotherms of 80 90 c km in the nphm and 35 c km in the skardu basin this relation suggests that rapid bedrock incision of at least 1 3 m ka has persisted within the nphm for the last 0 5 ma the acceleration of incision rates throughout the study area since 15 ka is likely to be a climatic signal that records an increase in the discharge and or sediment load of the indus river in the study area related to deglaciation of the surrounding terrane

fluid immiscibility in late alpine gold bearing veins eastern and northwestern european alps gold bearing quartz veins fill late alpine brittle structures in pennine nappes of austria in the tauern window and in northern italy the veins formed in the latter stages of uplift of the alps fluid inclusions in veins sampled from bockstein austria and valle anzasca italy have a wide variety of compositions ranging from aqueous brine about 5 wt nacl equiv to about 50 mol co2 at room temperature the inclusions range with increasing co2 content from two phase aqueous through three phase in which the co2 homogenizes to vapour to three phase with co2 homogenizing to liquid this wide range of inclusion compositions is interpreted as evidence for fluid immiscibility with most inclusions being accidental mixtures of the two end member immiscible fluids the homogenization temperatures of the aqueous inclusions 200 280 c gives the best estimate of temperature of formation of the veins vein formation fluid pressure at bockstein and valle anzasca was about 1 kbar and bockstein veins formed at lower pressure than valle anzasca veins fluid immiscibility may have contributed to deposition of gold at both valle anzasca and bockstein and possibly many other uplift related alpine gold localities

resistive dry lower crust in an active orogen nanga parbat northern pakistan abstract conductivity models beneath the nanga parbat haramosh massif nphm derived from magnetotelluric soundings reveal that there is no widespread interconnected conductive aqueous fluid to minimum depths of 40 km below sea level given the continuing tectonic denudation young granitic and migmatitic bodies indicating partial melt at shallow crustal depths and active seismicity this result is surprising in light of similar studies in active tectonic regimes elsewhere away from the nphm models reveal the usual conductive lower crust we propose that deep magmatic and metamorphic fluids are produced beneath nphm in isolated zones but that the active deformation permits their escape through the brittle ductile transition a magnetotelluric survey in an area as complicated as nanga parbat required the development of methodologies for utilizing standard two dimensional inversions in a three dimensional environment we show here how to identify which parts of the magnetotelluric responses are adequately represented with two dimensional approximations unlike previous efforts we do not attempt to create a set of generic rules that may be applicable to all geologic environments instead a procedure is outlined that can be tailored to each interpretation one important result of this work is that magnetotelluric data along a profile can be used to constrain structure off the ends of the profile

forcing of large scale cycles of coastal change at the entrance to willapa bay washington abstract anomalous morphological features within large estuaries may be 1 recorders of external forces that periodically overwhelm the normal morphodynamic responses to estuarine energy fluxes and 2 possible predictors of cycles of future coastal change at the entrance to willapa bay washington chronic beach erosion and frequent coastal flooding are related to the historical northward channel migration that destroyed the protective sand spits of cape shoalwater northward channel migration since the late 1800s conforms to the long term net sediment transport direction what requires explanation is periodic southward relocation of the trunk channel by as much as 5 km and attendant construction of moderately large sand spits on the north side of the bay such as kindred island tokeland peninsula and cape shoalwater both autocyclic and allocyclic processes may have been responsible for trunk channel realignment and associated spit deposition channel recycling may occur when the main channel becomes overextended to the north and the tidal flow is inefficient because of its decreased gradient and increased susceptibility to shoaling by the growth and migration of tidal sand ridges under those conditions trunk channel relocation would be facilitated by increased wave heights and water levels of el nino winter storms however co seismic subsidence is the most likely mechanism for abruptly increasing sand supply and longshore transport that would favor discrete periods of channel relocation and spit deposition unless external forcing changes sand supply and predominant sediment transport directions in the future the relative rise in sea level frequent winter storms and local deficit in the sand budget assure that beach erosion will continue at the mouth of this large estuary

neotectonics and glacial deformation in the karakoram mountains and nanga parbat himalaya abstract the karakoram mountains and the nanga parbat himalaya are one of the most rapidly rising mountain areas in the world with uplift rates in the order of 2 mm yr large scale regional warping is the most likely form of uplift with the greatest rates around the nanga parbat haramosh massif only two active faults have been recognised in the pakistan karakoram the rakhiot and the misgar valley fault the rakhiot fault zone is a neotectonic expression of the rapid uplift centred around the nanga parbat syntaxis deformation structures in quaternary and recent sediments in the rakhiot area are not produced solely by neotectonic processes but also by processes in the glacial depostional environment and slope related processes structures present vary from neotectonic shear zones folds thrusts and high angled faults glacially produced folds thrusts shears and joints and debris slides bounded by discrete shear zones the distinction between these structures is vital in making valid neotectonic models for high active mountain belts

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

crustal structure beneath namche barwa eastern himalayan syntaxis new insights from three dimensional magnetotelluric imaging the eastern terminations of the himalayan orogeny named namche barwa are considered a vital natural laboratory in the tibetan plateau for geodynamics due to its distinctive geological and geomorphological characteristics magnetotelluric mt data measured at 83 sites around the namche barwa are imaged by three dimensional 3d inversion to better reveal the crustal structure of the eastern himalaya the results show a complex and heterogeneous electrical structure beneath the namche barwa the electrical conductors distributed in the middle and lower crust around the namche barwa provide additional evidence for the crustal flow model if they are considered as some parts of the flow in a relatively large scale region the near surface resistivity model beneath the inner part of namche barwa conforms with the locations of hot spring and fluid inclusions the brittle ductile transition and the 300 c 400 c isotherm from previous hydrothermal studies relatively resistive upper crust 800 m is underlain by a more conductive middle to lower crust 80 m the electrical characteristics of the thermal structure at shallow depth indicate an accumulation of hydrous melting a localized conductive steep dipping zone for decompression melting consistent with the tectonic aneurysm model for explaining the exhumation mechanism of metamorphic rocks at namche barwa the results also imply that both surface processes and local tectonic responses play a vital role in the evolution of namche barwa an alternative hypothesis that the primary sustained heat source accounts for the local thermal rheological structure beneath namche barwa is also discussed

northern margin of the indian plate some litho tectonic constraints abstract the indus tsangpo suture zone represents crustal expression of a subduction zone in the himalaya all along its extension in kohistan ladakh and tibet the suture zone from south to north is constituted of litho tectonic assemblages referable to trench zone fore arc basin island arc and back arc basin these assemblages lie between the platform sediments deposited at the northern margin of indian and southern margin of tibet the trench assemblage consisting of ophiolitic assemblages exhibits high pressure glaucophanitic metamorphism the flysch sequence of the indus group represents fore arc sediments deposited in front of the ladakh magmatic arc comprising dras volcanics the ladakh plutonic complex and the khardung volcanics to the north of the magmatic arc the back arc basin assemblage represented by the shyok group consists of acid and basic volcanics and volcanoclastics intruded by granitic plutons the rocks of the arc and back arc region exhibit low pressure high temperature metamorphism the high pressure and low pressure metamorphic belts lying to the south and north respectively of the magmatic arc constitute paired metamorphic belts detailed analysis of tectonic and lithological characters of various litho tectonic units indicate that these developed at the northern margin of the indian plate during the mesozoic and early tertiary the miocene pliocene molassic rocks overlying various litho units unconformably were deposited after the collision of the indian and tibetan plates

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

shallow level metamorphic fluids in a high uplift rat metamorphic belt alpine schist new zealand fluids some of which are co2 rich up to 40 mol co2 and some of which are highly saline up to 18 wt nacl equivalent are trapped as fluid inclusions in quartz calcite metallic minerals veins which cross cut the pumpellyite actinolite to amphibolite facies rocks of the alpine schist fluids were commonly trapped as immiscible liquid vapour mixes in quartz and calcite showing open space growth textures fluid entrapment occurred at fluid pressures near 500 bars possibly as low as 150 bars at temperatures ranging from 260 to 330 c saline fluids may have formed by partitioning of dissolved salts into an aqueous phase on segregation of immiscible fluids from a low density co2 rich fluid calcite deposited by these fluids has 13c ranging from 8 4 to 11 5 and 18o from 4 to 13 isotopic data fluid compositions and mode of occurrence suggest that the fluids are derived from high grade metamorphic rocks fluid interaction with wall rock has caused biotite crystallization and or recrystallization in some rocks and retrogression of biotite to chlorite in other rocks fluid penetration through the rock is almost pervasive in many areas where permeability probably related to alpine fault activity has focussed fluids on a regional scale into fractured rocks the fluid flow process is made possible by high uplift rates in excess of 10 mm year bringing hot rocks near to the surface

25 years 1981 2005 of equilibrium line altitude and mass balance reconstruction on glacier blanc french alps using remote sensing methods and meteorological data annual equilibrium line altitude ela and surface mass balance of glacier blanc ecrins region french alps were reconstructed from a 25 year time series of satellite images 1981 2005 the remote sensing method used was based on identification of the snowline which is easy to discern on optical satellite images taken at the end of the ablation season in addition surface mass balances at the ela were reconstructed for the same period using meteorological data from three nearby weather stations a comparison of the two types of series reveals a correlation of r 0 67 at the 0 01 level of significance furthermore the surface mass balances obtained from remote sensing data are consistent with those obtained from field measurements on five other french glaciers r 0 76 p 0 01 also consistent for glacier blanc is the total mass loss 10 8mw e over the studied period however the surface mass balances obtained with the remote sensing method show lower interannual variability given that the remote sensing method is based on changes in the ela this difference probably results from the lower sensitivity of the surface mass balance to climate parameters at the ela

fluid evolution during uplift of the annapurna himal central nepal abstract fluid inclusions from post metamorphic quartz show that there has been considerable co 2 rich fluid flux during uplift of greenschist amphibolite facies rocks along the main central thrust mct maximum fluid co 2 content increased with metamorphic grade of the host rock ranging from 20 30 mole in the greenschist facies to both the north and south of the mct to 70 mole in the amphibolite facies the highest co 2 content is in late stage veins which cross cut uplift related schistosity in the sillimanite zone this contrasts with the syn metamorphic fluid which was probably dominantly aqueous fluid immiscibility occurred in quartz veins near the brittle ductile transition at 280 310 c and 700 300 bar fluid pressure an upper limit of 1600 bar lithostatic pressure was determined from a co 2 rich isochore the high thermal gradient implied by p t data is due to rapid uplift along the mct mct movement ceased in the miocene and the rocks have experienced slower uplift along a lower thermal gradient during this slower uplift ca na brines some with freezing point depression below 20 c have traversed the rock at first the brines mixed with co 2 then brines dominated until diluted by incursion of lowsalinity presumably meteoric water near the surface brines and co 2 may be reaching the surface today in diluted from as numerous warm and ambient springs brines were probably derived from connate fluids in the tibetan carbonate clastic sedimentary succession to the north of the mct co 2 was derived from metamorphosed equivalents of these sediments and perhaps from similar sediments beneath the mct

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

brittle and ductile deformation in a zone of rapid uplift central southern alps new zealand schists exposed in the central southern alps new zealand 1 5 km east of the alpine fault zone have been rapidly uplifted during the late cenozoic a regionally consistent sequence of mesoscopic structures discordant to the schistosity is recognized extending backward in time from recent brittle displacements of deglaciated surfaces through structures exhibiting brittle ductile transitional behaviour to ductile deformational features kinematic analysis of these structures gives consistent principal subhorizontal shortening directions similar to the present day principal horizontal shortening direction indicating their relation to late cenozoic uplift of the southern alps analysis of deformed veins suggests a minimum shortening strain of about 50 perpendicular to the foliation the veins crosscut upright mesoscopic to macroscopic folds which commonly develop high strain zones on their limbs within such zones a strong stretching lineation plunges gently sw approximately perpendicular to the stretching lineation in the mylonites along the alpine fault the folds and high strain zones do not appear to be related to late cenozoic uplift but may have originated during an earlier phase of dominantly strike slip motion fluid inclusion studies give depth temperature estimates of around 3 km and 285 c for the development of the brittle structures and 6 8 km at 310 350 c for the brittle ductile transition the deformed veins show evidence of extensive fluid infiltration during the later phases data from fluid inclusions and metamorphic assemblages give an estimate of 15 20 km and 400 450 c for their deformation these data combined with uplift rates determined by other studies allow the construction of a depth temperature time path which indicates nearly isothermal decompression associated with rapid uplift a shallow brittle ductile transition 6 8 km is consistent with numerical modeling of thermal and mechanical behavior of the crust during rapid uplift associated with continental collision and with the presence of high heat flow in the area because of the small temperature change over a large amount of decompression pressure may be an important factor in controlling the depth of the brittle ductile transition the marked temperature drop above the brittle ductile transition is thought to be enhanced by the influence of convection as an effective cooling mechanism

tectonic controls on the uplift of the nanga parbat massif pakistan himalayas cenozoic mountain belts like the himalayas contain regions that experienced rapid uplift in comparison with the areas around them1 whether this uplift occurred by buoyant rebound of previously thickened crust2 or during the crustal thickening process itself is uncertain3 4 here we show however that the 7 mm yr 1 recent uplift5 of the nanga parbat massif pakistan himalayas was accomplished during nw directed thrusting located along its western margin this 3 km wide liachar thrust zone operated from amphibolite facies to the present topographic surface and accommodates substantial crustal shortening the adjacent indus river valley itself cut by seismogenic faulting completely transects the massif showing that erosion keeps pace with geologically rapid thrust uplift6

geochronologic constraints on the tectonic evolution and exhumation of nanga parbat western himalaya syntaxis revisited abstract we examine the timing of deformation and exhumation of the nanga parbat haramosh massif in the western syntaxis of the himalaya this study presents geochronologic and thermochronologic data obtained from basement shear zone and intrusive units within the massif to reveal the cenozoic tectonic evolution of the massif and to document the extent of the plio pleistocene tectonic activity these results combined with structural and petrologic observations indicate that the western himalayan syntaxis was tectonically active for a protracted length of time and that the deformational succession was punctuated by three episodes since the beginning of the india asia collision 1 the western syntaxial indian plate rocks future nanga parbat underwent metamorphism melting and deformation during the initial collision of india with asia and the associated island arc the result of which is recorded as eocene to early miocene metamorphic and magmatic ages and oligocene cooling preserved in the indian co

tectonically driven fluid flow and gold mineralisation in active collisional orogenic belts comparison between new zealand and western himalaya abstract hydrothermal activity and mesothermal styled gold mineralisation occurs near the main topographic divide of most active or young collisional mountain belts the southern alps of new zealand is used in this study as a model for the mineralising processes the collisional tectonics results in a two sided wedge shaped orogen into which rock is transported horizontally upper crustal rocks pass through the orogen and leave the orogen by erosion whereas lower crustal rocks are deformed into the mountain roots high relief drives meteoric water flow to near the brittle ductile transition lower to upper greenschist facies metamorphic reactions driven by deformation at the crustal decollement and in the root release water rich fluids that rise through the orogen intimate chemical interaction between fluid and rock results in dissolution and later precipitation of gold arsenic and sulphur fluid flow and mineralisation in the topographic divide region is facilitated by a network of steeply dipping faults and associated rock damage zones where oblique strike slip faults intersect the thrust faults that strike subparallel to the main mountain range the nanga parbat massif of the western himalaya is an example of an active collisional zone which hosts hydrothermal activity but no gold mineralisation the lack of gold mineralisation is due to the following factors co 2 dominated rising metamorphic fluid in dehydrated amphibolite granulite facies metamorphic rocks does not dissolve gold and arsenic hot up to 400 c meteoric water confined to fractures in the gneiss limits dissolution of gold and arsenic low density of hot water dry steam and low reduced sulphur content of fluid restrict solubility of gold and arsenic absence of fracture networks in the core of the massif and the small volumes of circulating fluid limit metal concentration and lack of reactive rock compositions limits chemically mediated metal deposition

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

evolution of fluid driving forces and composition within collisional orogens subaerial collisional mountain belts have a predictable asymmetric two sided wedge geometry the major driving forces for crustal fluid flow in this framework arc thermal and topographic gradients it is possible to predict both a time averaged fluid state and the evolution of the fluid regime during orogenesis with three distinct fluid flow regimes the outboard toe where material is incorporated into the orogen a transitional zone of concentrated deformation and a zone of rapid exhumation along the inboard slope adjacent to the indentor as rocks move into the outboard wedge relatively low temperature compaction and head driven fluid flow dominates mid crustal material undergoes disequilibrium dehydration as rock fluid packets move into the transition zone producing a dominantly aqueous metamorphic fluid in the inboard region rapid uplift produces geothermal gradients in excess of 80 c km which encourage vigorous free convection advecting fluids evolve through immiscibility towards increasing co2 content during uplift of the rock fluid packets mixing of thermally driven and head driven fluids occurs at depths of 5 10 km the southern alps of new zealand the european alps and the himalaya represent variants of this orogenic hydrothermal system

slope failure and denudation in the western himalaya slope failures glaciers and rivers constitute the three main agents of denudation in the himalaya failure of slopes is strongly controlled by bedrock geology especially at plate terrane boundaries although climatic and seismic controls of failure also occur slope failure complexes in the western himalaya studied for this report include the pakhar kaghan nanga parbat and atabad hunza areas with 23 different slope failures reported within all the complexes quantification of denudation by mass movement requires measurement of volumes and determination of timing of sediment emplacement and removal where possible to obtain better data on recurrence intervals and total geomorphic work performed in formation of the landscape the relation of mass movement to overall denudation by glaciers and rivers and its role in catastrophic floods and debris entrainment is assessed

late miocene to early pliocene tectonometamorphism and cooling in south central karakorum and indus tsangpo suture chogo lungma area ne pakistan abstract the chogo lungma glacier is located at the northeastern edge of the nanga parbat haramosh spur where the ladakh kohistan arc formations are laminated between the karakorum and high himalaya units in the karakorum metamorphic complex metamorphism of a pelitic and granitic protolith took place in two tectonometamorphic phases isoclinal folds 700 c 1 gpa were followed by doming 630 700 c 400 750 mpa in a compressional climax lemennicier et al 1996 one hornblende and two biotites associated to syntectonic magmatism with mantle affinities contemporaneous of doming give cooling ages between 3 0 and 7 7 ma a muscovite from an orthogneiss in the karakorum gives an age of 5 ma fast cooling 70 110 k ma has prevailed ever since two muscovites from a foliated intrusion emplaced on the thrust of the ladakh kohistan arc over the high himalaya crystallines have ages of 8 2 and 9 ma despite being collected in the same locality dating the thrust at just before 9 ma all this points to a coeval tectonometamorphism and thrusting in that area during the tortonian

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

geology of the northern part of the nanga parbat massif northern pakistan and its implications for himalayan tectonics the northern outcrop termination of indian continental crust lies at the nanga parbat massif from where this contribution presents new field data the tectonic contact with the structurally overlying kohistan island arc is concordant and ductile is associated with interleaving of nanga parbat and kohistan lithologies and may be correlated with the main mantle thrust found elsewhere in the nw himalayas this ductile shear zone is locally overprinted by cataclastic faults associated with exhumation of the massif but overall the northern outcrop termination of the massif is controlled by erosion through a gently northward plunging antiformal structure this folds both the main mantle thrust and the underlying concordant 9layered unit9 of the nanga parbat basement thus there is no indication that the massif acted as a promontory to the indian continent during collision nor that it is a structure entirely bound by neotectonic faults ductile shear fabrics associated with the 9main mantle thrust9 are cross cut by leucogranite sheets and pegmatites these may represent the stockwork to a significant crustal melt granite body described here in the northern massif this jutial granite shows many geochemical characteristics in common with similar bodies in the high himalayas which are consistent with anatexis of the buried indian continental basement rocks however the granite is enriched in heat producing elements particularly th 22 ppm and shows extremely high 87 sr 86 sr ratios 0 88 the high concentrations of radiogenic sr are also an attribute of a suite of hitherto enigmatic leucogranitic pegmatites that laces the nanga parbat massif suggesting that these may represent a stockwork to a largely buried body of which the jutial granite is a small exposure the enrichment in heat producing elements within the granite may reflect similarly high heat production in the source indian continental crust requiring in turn a fundamental re examination of the thermal evolution of this crust during himalayan metamorphism and exhumation

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