the closing of tethys and the tectonics of the himalaya recent geological and geophysical data from southern tibet allow refinement of models for the closing of southern neo tethys and formation of the himalaya shelf sediments of the indian passive continental margin which pass northward into deep sea tethyan sediments of the indus tsangpo suture zone were deposited in the late cretaceous an andean type margin with a 2 500 km long trans himalayan kohistan ladakh gangdese granitoid batholith formed parallel to the southern margin of the lhasa block together with extensive andesites rhyolites and ignimbrites lingzizong formation the southern part of the lhasa block was uplifted deformed and eroded between the cenomanian and the eocene in the western himalaya the kohistan island arc became accreted to the northern plate at this time the northern part of the lhasa block was affected by jurassic metamorphism and plutonism associated with the mid jurassic closure of the bangong nujiang suture zone to the north the timing of collision between the two continental plates ca 50 40 ma marking the closing of tethys is shown by 1 the change from marine flysch like to continental molasse like sedimentation in the indus tsangpo suture zone 2 the end of gangdese i type granitoid injection 3 eocene s type anatectic granites and migmatites in the lhasa block and 4 the start of compressional tectonics in the tibetan tethys and indus tsangpo suture zone south facing folds south directed thrusts after the eocene closure of tethys deformation spread southward across the tibetan tethys zone to the high himalaya deep crustal thrusting barrovian metamorphism migmatization and generation of oligocene miocene leucogranites were accompanied by south verging recumbent nappes inverting metamorphic isograds and by south directed intracontinental shear zones associated with the main central thrust continued convergence in the late tertiary resulted in large scale north directed backthrusting along the indus tsangpo suture zone more than 500 km shortening is recorded in the foreland thrust zones of the indian plate south of the suture and 150 km shortening is recorded across the indian shelf zanskar range and the indus suture in ladakh there was also large scale shortening of the karakoram and tibetan microplates north of the suture as much as 1 000 km shortening occurred in tibet the more recent deformation however involved the spreading of this thickened crust and the lateral motion of the tibetan block along major approximately east west trending strike slip fault zones

object based classification of sub bottom profiling data for benthic habitat mapping comparison with sidescan and roxann in a greek shallow water habitat abstract although ground discrimination systems and multi beam echo sounders tend to be the preferred tools towards gaining knowledge about the seafloor numerous surveys have been and are still being performed by simultaneously using conventional sidescan sonars ssss and sub bottom profilers sbps this is in respect of gaining fast wide scale three dimensional imaging of the seafloor and its substrate extracting maximum value from a single time limited survey the combination of these two systems offers good knowledge of both the stratigraphy and the habitat extents on the seabed aspects often linked to each other however a basic drawback is the inconsistency between their mapping scales as sss produces high resolution backscatter maps and sbp produces substrata information of high vertical but very low horizontal density in this work 100 khz sss and 3 5 khz sbp data collected simultaneously during a geophysical survey at a 5 5 3 3 km shallow 10 50 m depth marine protected area in lourdas gulf kefalonia island greece underwent post processing and analysis to extract numerous statistical features from both the seafloor and its substrate towards automated seafloor classification the sss mosaic image was subjected to segmentation coupling the mean shift algorithm and unsupervised classification the sbp images were processed using edge enhancement detection techniques and numerous features were extracted regarding the acoustic appearance transparency and density of the automatically detected seismic reflectors supervised classification of the sbp derivatives exhibited their high discrimination ability between different sea bed types making them suitable for ground discrimination linking of the sbp classes to the sss segments object based analysis led to full coverage high detailed benthic habitat maps training of the classifiers was carried out using data points in proximity to underwater video inspected areas while validation was performed using a manual habitat map made by expert interpreters three marine habitat classification schemes have been examined separately namely natura eunis and a custom one successively including more habitat types in a hierarchical manner as to validate the method under different complexity levels the sss mosaic as well as an independent data set acquired using roxann acoustic ground discrimination system were also used each individually to classify lourdas gulf in yet again an object based manner the latter showed that sbp derivatives led to an equally significant and in most cases better classification of benthic habitats compared to those produced by the widely tested and documented sss and roxann systems implying that they deserve further exploitation

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

stress field evolution in the northwest himalayan syntaxis northern pakistan 1 we have conducted a systematic inversion of striated fault planes throughout northern pakistan in order to better depict the temporal and spatial variations in stress patterns two domains are evidenced at a regional scale separated by the active raikhot fault the western boundary of the nanga parbat spur west of this fault a wrench type stress field with 1 axis oriented around n s predominates in the karakorum and in kohistan it predates pliocene quaternary exhumation of nanga parbat and corresponds to the miocene or earlier regional stress field related to indian asian convergence east of the raikhot fault compression parallel to the belt accounts for initiation of the nanga parbat anticlinorium after 5 ma it is followed by predominant post 2 ma extension both parallel to the belt and nne ssw oriented thus in the n w himalayan syntaxis multidirectional extension is juxtaposed on short timescales to shortening either parallel or perpendicular to the belt such juxtaposition could be characteristic of strain and stress partitioning during oblique convergence

orographic channeling of a cold front by the pyrenees abstract the channeling effect of the pyrenees on a cold front is illustrated using high resolution surface data satellite data support the analysis of the surface data and show that the surface front is trapped to a significant degree in the vicinity of the mountains

seismic stratigraphy of lake huron georgian bay and postglacial lake level history five seismic reflectors in the basinal sedimentary section have been identified as representing erosional surfaces in shoaler regions of the lake basins and can be traced throughout most of the study area the reflectors representing these erosional surfaces and their conformable equivalents in the deep lake basins are caused by intervals of coarser grain size in the sediments and are thought to represent lowering of lake levels prior to and following the main algonquin highstand about 10 2 11 0 ka these reflectors are used to define seismic sequences in the postglacial sedimentary fill of the basins two additional erosional surfaces which closely follow the initial fall of the main algonquin lake level are most clearly seen in thicker sections found in the northern part of the basins the two oldest pre main algonquin sequences appear to onlap highs and fill in lows within the basins whereas the younger sequences associated with the main algonquin through mattawa times tend to drape the

the record of glacial lake champagne in kusawa lake southwestern yukon territory late pleistocene glaciers dammed glacial lake champagne in the valley of dezadeash river between a westward flowing glacier in the takhini valley and eastward flowing glaciers from the st elias complex modern kusawa lake lies in the southern extension of lake champagne geophysical and geomorphic evidence documents the deglaciation of the lake the presence of lake champagne and the postglacial sedimentary environment of the basin during the main phase of lake champagne the water level stood at 772 m in the northern part of kusawa lake and 756 m in northern dezadeash valley both probably controlled by a spillway floored at 756 m to the north into the nordenskiold river this indicates differential isostatic rebound of 0 2 m km from south to north at that time a trunk glacier occupied the southern portion of kusawa lake depositing a thick sequence of sediment in the basin a glacier in the primrose valley and the takhini trunk glacier built large deltas into lake champagne subsequently the level

tectonic framework of the indus and shyok suture zones in eastern ladakh northwest himalaya abstract three different phases of plutonic volcanic activity viz 1 1 cretaceous volcanics of the dras and luzarmu formations 2 2 early tertiary granitoids of the ladakh plutonic complex 3 3 oligocene acid volcanics and dykes of the khardung formation have been recognised in the ladakh magmatic arc the dras formation of the indus suture zone and the luzarmu formation of the shyok suture zone were one stratigraphic unit into which granitoids of the ladakh plutonic complex intruded the rocks of the shyok suture zone are interpreted to represent the tectonised remainder of a marginal back arc basin the closure of the marginal basin occurred at the eocene oligocene time boundary and crustal shortening was responsible for generation of neogene 2 mica granites of the karakoram plutonic complex and regional metamorphism of the pangong tso group

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

an observational and numerical study of an intense landfalling cold front along the northwest coast of the united states during coast iop 2 abstract this paper presents an observational and numerical study of an intense wintertime cold front that made landfall along the northwest coast of the united states during iop 2 3 4 dec 1993 of the coastal observation and simulation with topography experiment observations suggest that the offshore frontal zone was associated with two transitions the first characterized by a substantial temperature gradient a nearly vertically oriented wind shift from southwesterly ahead to westerly behind and a convective rainband while the second transition had a slantwise wind shift zone from westerly ahead to northwesterly behind the frontal zone was quite narrow 5 km wide and nearly vertical below 850 mb and its width increased by 1 2 orders of magnitude above 850 mb well before the frontal landfall low level flow to the west of the olympics was associated with geostrophic balance in the cross shore direction and downgradient acceleration in the alongshore direction which contributed to the formation

a jurassic cretaceous island arc in the ladakh himalayas abstract the ladakh mesozoic ophiolite belt western himalaya contains a pile of volcanic thrust sheets dras unit which differ significantly in structure and composition from the ophiolitic melange zones the dras unit is composed of pillow lavas doleritic sills very irregular basaltic basaltic andesites and dacitic flows intercalated with pyroclastics volcanoclastic sediments and radiolarian cherts according to fossil evidence this volcanism must have been active between upper jurassic and upper cretaceous the presence of relict primary minerals such as magnesiochromite clinopyroxene hastingsitic hornblende and ti magnetite as well as distinctive bulk chemistries suggests that the volcanics belong to island arc tholeiite and to calc alkaline rock series typical of present island arcs in the caribbean and pacific model calculations incorporating probed phenocryst phases indicate that in addition to olivine clinopyroxene and plagioclase amphibole and titanomagnetite are crucial fractionating phases in the development of the dacites from a primitive tholeiitic melt the latter process must have taken place at about 1000 c and at moderate depth of 5 15 km within or underneath the island arc today hornblende bearing mafic cumulates appear in the vicinity of kargil within and close to the dras volcanics in a sr evolution diagram the dras volcanics have yielded a pseudo isochron with a low initial 87 sr 86 sr ratio of 0 7035 0 0003 which is in the same range as the mean of modern island arc volcanics however a geologically unrealistic age of 263 m y is obtained from the slope of this isochron the upper mantle is regarded as the source material for the island arc tholeiitic magmas enrichment in k ba sr and lree supports the involvement of components derived from dehydration or incipient melting of subducted tethyan oceanic crust in the mantle

pathways and processes associated with the transport of groundwater in deltaic systems summary rivers are considered to be the primary means driving hydrological and geochemical fluxes between the continents and the ocean however it is unclear how well surface water fluxes represent total fluxes or whether more diffuse subterranean fluxes of river water to the coastal ocean occur this question is important in light of research demonstrating that submarine groundwater discharge sgd is important for geochemical and hydrological fluxes here we examine the pathways and potential magnitude of the role that sgd plays in the mississippi river delta mrd the largest delta in north america we present multiple independent lines of evidence demonstrating a hydrological connection between the mississippi river mr and the mrd evidence includes hydrological budgets demonstrating downstream water losses from the mr which are unexplained and are of the same magnitude as water sources to adjacent coastal bays of the mrd well data indicating a correlation between groundwater height and the stage of the mr and excess 222 rn inventories exceeding that expected from in situ production implying an advective i e groundwater source to coastal bays sgd likely flows from the mr to its delta via paleochannels and other buried sand bodies seismic data indicates that such features are common whereas resistivity data suggest the intrusion of low salinity water to coastal bays adjacent to the river these results may be applicable to other deltas worldwide as many of the world largest rivers have deltas with numerous abandoned distributaries that could act as conduits for groundwater

the karakorum block in central asia from ordovician to cretaceous abstract the karakorum block records a predominantly marine ordovician to cretaceous sedimentary history six major sedimentary cycles are recognised the oldest sediments early ordovician transgress over a crystalline basement the 1 km thick ordovician silurian mostly shaly succession contains rare carbonate intercalations in the early devonian a wide peritidal platform spread over the craton sedimentation rates were low 10 20 m ma and upper devonian probable lower carboniferous carbonates and clastics rest unconformably on the early devonian carbonates no evidence has been found for either late carboniferous or glaciogenic deposits sedimentation rates increased during the permian up to 50 m ma with thicknesses between 1 and 2 5 km three steps are identified 1 a huge alluvial to marginal marine terrigenous prism aggraded during the asselian sakmarian 2 the artinskian murgabian is characterised by local emergence and erosion linked to extension with block rotations 3 greater differentiation occurred from late permian to middle triassic when a peritidal carbonate flat developed in the southwest facing a deeper basin to the northeast carbonate sediments prevailed throughout the carnian norian the permo triassic evolution is interpreted as the passive margin stage of the karakorum block which previously belonged to the perigondwanian fringe when like mega lhasa it drifted northward on the tethyan transit plate mega lhasa is considered as a collage of blocks possibly separated by thinned crust or short lived seas with ocean crust quartzo lithic sandstones with grains of mafic volcanics and serpentinite overlain with gentle unconformity by pliensbachian toarcian red sandstones with sedimentary and metasedimentary clasts record the eo cimmerian deformation in the karakorum this orogenic episode was over by the aalenian when a shallow water carbonate ramp aggraded onto the previously emergent area the pre barremian upper jurassic and lower cretaceous are poorly documented in post barremian times the sedimentary succession of n karakorum was severely deformed in huge thrust sheets including slabs of crystalline basement a coarse conglomerate of mid cretaceous age sealed the thrust sheet edifice finally isolated campanian pelagic mudstones are recorded anticlockwise rotation of mega lhasa followed the late triassic docking of the iranian spur using the latter as pivot the rotation was completed during the middle jurassic when se pamir shaksgam and karakorum joined the qiangtang more closely assembling mega lhasa as it approached the asian margin

depositional features of co genetic turbidite debrite beds and possible mechanisms for their formation in distal lobated bodies beyond the base of slope ulleung basin east sea japan sea abstract a detailed analysis of the mr1 11 12 khz sonar images chirp 2 7 khz profiles core sediments and 14 c ages from the latest quaternary lobated bodies lb on the deep 2100 m water depth basin plain of the western ulleung basin reveals depositional features and context of co genetic turbidite debrite beds in the lb on the distal setting and a plausible mechanism for generating these beds eight lb are present in the basin plain ca 30 60 km beyond the base of slope and were generally deposited retrogressively older and more distal lb 1 4 have large dimensions 27 km long 15 25 km wide in contrast younger and less distal lb 5 8 are small 8 8 31 5 km long 1 2 12 km the muddier larger lb 1 and 2 were most likely originated from the relatively large scale sediment failures on the muddy upper slopes 350 400 m water depth between 18 5 and 20 0 cal ka b p on other hand the sandier smaller lb 6 and 7 were deposited between 17 0 and 17 5 cal ka b p probably by the relatively small scale sediment failures on the sandy uppermost slope shallower than 350 400 m water depth in lb 1 a lower sandy mud turbidite is transitional upward into an upper mud matrix debrite having small rounded mud clasts in contrast lb 6 exhibits a gradual upward change from a lower clay poor sandy turbidite to an upper clay rich sand matrix debrite with large interlocking mud clasts each mixed bed in lb 1 and 6 can represent a co genetic or linked turbidite debrite bed formed by the down dip flow transformation from turbidity current to debris flow at a point during the same event the abundant large scale up to 20 25 m deep 3 5 km long erosions of fine grained substrates near the base of slope area suggest that the down dip transformation was driven by incorporation of mud via erosional bulking by turbidity currents reaching the base of slope area the different clay sand content and size shape of mud clasts in the co genetic turbidite debrite beds between lb 1 and 6 imply that the composition sandy or muddy and dimension of initial turbidity current approaching the base of slope the volume of eroded masses from the fine grained substrates and the transport distance of sediment gravity flows from the erosional areas of muddy substrates can be all important factors controlling the depositional styles of co genetic turbidite debrite beds

the transhimalaya gangdese plutonism in the ladakh region a upb and rbsr study abstract the age and origin of the transhimalaya gangdese plutonic belt in the ladakh area has been studied by high resolution u pb analyses of accessory minerals zircon and monazite allanite and rb sr measurements on whole rock samples the ages determined of 101 2m y for a granodiorite and of 60 7 0 4m y for a granite substantiate that the transhimalaya plutonism was active at least in mid cretaceous albian and earliest tertiary palaeocene times a rb sr isochron of 73 4 2 4m y might be fortuitous because the rb sr systematics shows important heterogeneities on the whole rock scale the inherited radiogenic lead in zircon demonstrates that anatexis of continental crust was involved in magma genesis the thus recycled continental material was heterogeneous with respect to its primary ages and or metamorphic history the approximate minimum ages of the continental sources range from 350 to 590 m y the 101 2m y old transhimalaya granodiorite which intrudes a series of mainly basaltic island arc rocks dras series shows that this island arc was attached to the continental margin at that time this is consistent with the hypothesis that the ladakh tethys closed through two subduction regimes 1 an early cretaceous subduction which formed the dras island arc and 2 a late cretaceous to palaeocene subduction at the continental margin which caused the emplacement of the transhimalaya plutonic belt

normal incidence measurement in a subaqueous sand dune field in the south china sea regions with subaqueous sand dunes have been discovered on the upper continental slope of the northern south china sea these large subaqueous sand dunes are expected to cause errors in the measurement of normal incidence reflection this letter presents experiment results of two normal incidence survey tracks conducted in 2013 and the errors in reflection coefficient estimation and the resulting sediment properties induced by sand dune bedforms the results demonstrate that the reflected energy is focused and scattered by different parts of sand dune bedforms and that they produce significant variation in the estimated reflection coefficients and the inverted geoacoustic properties

late glacial and holocene sedimentary environments of quesnel lake british columbia abstract at 512 m quesnel lake is the third deepest in north america and at 100 km long its drainage basin spans from the arid interior plateau to the high mountains of the eastern cordillera where small glaciers are a significant source of sediment in most of the lake sediment is 0 to 40 m thick reaching a maximum of just over 100 m thick near the junction of the three arms cores from three locations in the lake provide evidence that the entire holocene record is contained in the upper 4 to 6 m of the sedimentary record where rates of accumulation have been constant or have decreased slowly the highest rates 0 35 to 0 72 mm a occur near points of inflow while the lowest rate 0 22 mm a occurs in a sheltered environment with limited inflow and significant hypolimnic circulation which may flush water and suspended sediment from the water column late pleistocene sediment beneath has a similar acoustic signature to the cored holocene record above suggesting that the sedimentary processes governing its deposition were not greatly different than in the present lake but that extensive glacial and paraglacial sources contributed to a significantly higher rate of accumulation mazama ash analyzed from two locations near points of inflow has an age of 7576 60 cal bp according to our chronology vivianite which is uncommon in lakes of the cordillera occurs in the middle of the cores mainly associated with macroscopic wood fragments and indicates reducing conditions within the sediment

incipient india eurasia collision and plutonism the lower cenozoic batura granites hunza karakorum north pakistan plutonism of the karakorum north of the india eurasia suture zone comprises two major intrusive stages the oldest mid cretaceous predates the collision the youngest miocene is post suturing in between lower cenozoic plutonism roughly syn suturing and represented by the batura complex is made up of a few small and usually undeformed plutons the complex has a subalkaline i e intermediate between alkaline and calc alkaline and ferriferous association dominated by light coloured metaluminous and slightly peraluminous granites and adamellites with biotite amphibole titanite whole rock rb sr isochron ages of 63 ma this study and 43 ma debon et al 1987b have been obtained for two plutons with rather low initial 87 sr 86 sr ratios 0 7050 0 7056 a comparison with granitoids of similar age from kohistan suggests that the complex relates to the subduction of the tethys ocean and originates from a mantle source with but small crustal contribution through a two stage melting process the apparently limited extent of lower cenozoic plutonism in the karakorum contrasts with its wider development in the transhimalaya and kohistan this contrast could be partly accounted for by changes in tectonic and magmatic suduction related processes after the initial contact between india and eurasia was established in the nw himalaya

forward modeling for marine sediment characterization using chirp sonars this paper investigates the forward modeling of chirp sonar data for the quantitative characterization of marine subbottom sediment between 1 and 10 khz the forward modeling based on a transfer function approach included impacts of layering or impedance mismatch attenuation roughness and transitional layers i e continuous impedance variations the presented approach provided the best compromise between the number of available geoacoustic parameters from chirp sonar data and the subbottom modeling accuracy the forward model was tested on deep sea chirp sonar data acquired at a central frequency of 3 5 khz comparisons between synthetic and experimental seismograms showed good agreement for the first 15 m of buried layers performance of the inversion using this forward model was also examined through sensitivity analysis the results suggested that estimations of layer thickness impedance and transitional layer thickness were robust whereas roughness and attenuation estimations were subject to wavelength and layer thickness conditions

the northern suture pakistan margin of a cretaceous island arc the northern suture is a fault separating the cretaceous kohistan island arc terrain northwest himalayas from palaeozoic sediments of the asian plate to the north the kohistan arc includes volcanic and sedimentary rocks andesitic lavas tuffs volcaniclastics slates and limestones metamorphosed to greenschist facies and intruded by the two phase kohistan batholith asian continental margin sediments are mainly of shelf type are variably metamorphosed and intruded by the karakoram batholith the northern suture is a zone of melange from 150 m to 4 km wide and contains blocks of volcanic greenstone limestone red shale conglomerate quartzite and serpentinite in a slate matrix it has a strong planar fabric but in many places bedding is preserved in blocks and matrix and depositional rather than tectonic contacts are seen between the two the melange is inferred to be an olistostrome largely derived from the kohistan arc formed in a small back arc basin between kohistan and asia limestone blocks in the melange are dated as aptian albian post tectonic intrusions yield radiometric ages from 111 to 62 ma the northern suture therefore probably formed in the early late cretaceous during closure of the back arc basin the tethys ocean lay south of kohistan where the main mantle thrust represents the westward continuation of the indus tsangpo suture

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

the north karakorum side of the central asia geopuzzle an italian geological team visited a remote and in part never studied area in the northern hunza region pakistan which represents the link between the karakorum and pamir ranges the north karakorum sequence commences in the permian with terrigenous sediments followed by shallow to deep marine carbonates deposited on a newly formed passive margin deep water sedimentation continued till the end of the middle triassic when carbonate platform conditions resumed an episode of deltaic red sandstones with orogenic provenance is interbedded in the liassic and it is transgressed by a middle to upper jurassic shallow water marine unit eventually all of the sequence was faulted and folded with weak metamorphic imprint before fluviatile red polygenic conglomerates sealed the succession in a spectacular unconformity the north karakorum provides an example of a microplate that rifted away from gondwana in the permian reached deep marine conditions in the early triassic and marginally recorded compressive movements in the liassic a subsequent orogenic episode points to a reorganization of the southern asian margin possibly around middle cretaceous time finally the north karakorum was affected by strong fold thrust deformation and low to very low grade metamorphism in the cainozoic related to the india asia collision

late quaternary sedimentation in the ulleung interplain gap east sea korea the ulleung interplain gap uig is a deep 2300 2700 m passage which has served as a conduit for deep water circulation between the ulleung and japan basins a detailed analysis of chirp 2 7 khz subbottom profiles ca 6270 linekm and nine sediment cores 8 6 11 4 m long together with age data of tephra layers and four ams 14 c from the uig and the adjacent areas reveals complex sedimentation caused by an interaction between bottom currents and mass flows during the lastand post glacial periods from high resolution subbottom data rock basement slide slump rock fall deposits mass flow chutes channels mass flow deposits bottom current deposits and a large scale bottom current channel system are recognized core sediments consist of various deposits of turbidites muddy contourites manganiferous contourites and pelagic hemipelagic sediments based on vertical distribution of sedimentary facies together with a chronostratigraphic framework core sediments can be divided into units i f15 ka the extensive mass flow deposits with slope failures on the entire slopes of topographic highs around the uig and the dominant turbidites in unit ii f15 ka suggest that a relatively large amount of sediment was delivered into the uig by frequent mass flows recurrence intervals of ca 250 500 years in the upper unit ii during the last glacial period erosion or hampered sedimentation by bottom currents is indicated by the truncated reflectors of channel walls and muddy manganiferous contourites in the ulleung interplain channel uic along the uig interbedded turbidites in the uic floor reflect that some large scale mass flows intermittently entered into the uic the uic has an asymmetric channel flank geometry the southeastern flank shows a gentle wide mound morphology of mass flow deposits derived from large scale slope failures on the slopes of the oki bank reflecting a dominance of downslope gravitational processes over alongslope bottom currents in contrast the northwestern flank is characterized by a narrow steep geometry of mass flow deposits where a relatively small amount of sediment derived from the slopes of the south korea plateau could not overcome bottom current activity the dominant muddy and manganiferous contourites with rare turbidites in unit i f15 ka reflect intensified bottom currents and infrequent slope failures recurrence intervals of ca 1700 5000 years during the post glacial period these

sediment waves in a modern high energy glacilacustrine environment a 4 7 km2 field of sediment waves occurs in front of the slims river delta in kluane lake the largest lake in the yukon territory slims river heads in the kaskawulsh glacier part of the st elias ice field and discharges up to 400 m3 s 1 of water with suspended sediment concentrations of up to 7 g l 1 the 19 km long sandur of slims river was created in the past 400 years since kaskawulsh glacier advanced and dammed the lake and the sandur has advanced into kluane lake at an average rate of 48 m a 1 however this rate is decreasing as flow is diverted from slims river because of the retreat of the kaskawulsh glacier the sandur and a road constructed on the delta remove coarse grained sediment so the river delivers dominantly mud to the lake inflow during summer generates quasi continuous turbidity currents with velocities up to 0 6 m s 1 the front of the delta consists of a plane surface sloping lakeward at 0 0188 1 08 a field of sediment waves averaging 130 m in length and 2 3 m in amplitude has developed on this surface slopes on the waves vary from 0 067 3 83 i e sloping in the opposite direction to the regional slope to 0 135 7 69 the internal structure of the sediment waves as documented by seismic profiling shows that sedimentation on the stoss portion of the wave averages 2 7 times that on the lee portion rates of sediment accumulation in the wave field are about 0 3 m a 1 so these lacustrine waves have formed in a much shorter period of time less than 200 years and are advancing upslope towards the delta much more quickly 1 to 2 m a 1 than typical marine sediment waves these waves formed on the flat surface of the lake floor apparently in the absence of pre existing forms and they are altered and destroyed as the wave field advances and the characteristics of the turbidity currents change

the papal front of 3 may 1987 a remarkable example of frontogenesis near the alps all available routinely collected surface data are used to document the development of the papal front which crossed southern germany on 3 may 1987 causing casualities and damage objective analyses on isentropic surfaces initialized with the european aerological data indicate that the development of the violent mesoscale front which exhibited squall line characteristics began when a distinct mid troposopheric anomaly of potential vorticity reached the north western rim of the alpine arc the forced uplift ahead of the associated shortwave trough combined with ageostrophic motions due to a jet streak at higher levels apparently provided a trigger for deep convection as was observed over the alpine foreland numerical simulations with a dry hydrostatic model indicate the relative importance of the synoptic scale forcing and the alpine orography for the generation of the papal front a westerly orographic jet over the foreland below crest height only develops in the simulation with full alps and is corroborated by the few mountain wind observations that are available a comparison with studies of frontal propagation along other mountain ranges reveals that the routine network in the alpine region and its surroundings is at least of similar density but so far hardly used for frontal case studies it is concluded that a series of routine data case studies could help to determine the variability of frontal progression along the alps and thus provide guidance when assessing the significance of single events particularly those sampled during special observation programmes

high resolution 2 7 khz acoustic and geometric characters of submarine creep deposits in the south korea plateau east sea a synthesis of high resolution chirp 2 7 khz seismic profiles in the south korea plateau reveals that large masses of wavy stratified sediment 60 90 m thick cover broad gently sloping 0 5 ridges in water depths of 1000 2000 m the wavy stratified sediment wss is characterized by wavy 0 2 5 km in wavelength and 15 m in relief continuous reflective layers with a basal deformed zone that overlies undeformed strong reflectors the wss exhibits systematic variation in wave dimensions and thickness of internal reflective layers with changes in slope gradient the troughs of the waves are commonly associated with internal growth faults and wave amplitude generally increases with subbottom depth on steep slopes around the ridges the wss masses are bounded downslope by slide and slump deposits including slightly translated or rotated wss blocks the acoustic and geometric characters and association with downslope slides and slumps on the steeper slopes suggest that the wss masses were most probably formed by slow creep movement before slope failure in the absence of significant sediment input to the south korea plateau the deep 1000 2000 m in water depth mass movements were probably triggered by earthquakes that have occurred frequently in this region some slightly displaced intact wss blocks in the associated slides and slumps downslope reflect a progressive evolution from submarine creep into slide and slump

acoustic and physical property relationships in marine sediment in situ sediment acoustic impedance measured from a ship underway is being used to infer the physical properties of the sea bed these inferences rely on published regression relationships developed to estimate impedance from sediment density or porosity thus the equations must be rearranged to yield the desired parameter when impedance is known rearranging or inverting regression equations is not a valid technique it is justified only when properly derived equations are unavailable herein are regressions of sediment density porosity and mean grain size on impedance to complement relationships already in the literature presented also are data and methods to place confidence limits on the predictions

geo tectonic framework of the himalaya of n pakistan in the karakorum range there is a structurally complicated cretaceous are comprising the kohistan sequence on its northern side the northern suture consists of a mega melange and is bounded to the s by tightly folded pillow bearing volcanics and sediments to the s the kohistan plutonic belt consists of southwards a early foliated and late post tectonic tonalites and diorites b aplites and pegmatites up to 30 of rock volume c basic dykes up to 10 m thick d the chilas complex a stratiform cumulate body over 300 km long and 8 km thick chromite layered dunites gabbros and norites with a low pressure granulite facies mineral fabric of tectonic origin e an amphibolite belt with a complex mixture of other rocks and f the jijal complex a 200 km 2 tectonic wedge of high pressure granulites and chromite layered dunites cumulate graded units in the chilas complex show that it is folded by an isoclinal anticline f 1 the mid upper crust of the are is folded by a 50 km half wavelength f 2 syncline the whole kohistan sequence with its two phases of isoclinal folds was tilted during himalayan collision so that the structures are now subvertical the southern suture main mantle thrust has a wedge of glaucophane schists the indian plate contains a basement of psammites and schists intruded by cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

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

brittle fault evolution of the montreal area st lawrence lowlands canada rift related structural inheritance and tectonism approached by palaeostress analysis the montreal area belongs to the st lawrence lowlands a cambrian early ordovician passive margin of the iapetus ocean later covered by appalachian middle to upper ordovician foreland deposits a structural and palaeostress analysis has been carried out in order to reconstruct its tectonic evolution the structural map has been revised with new data palaeostresses are reconstructed based on inversion of fault slip data and these results are independently corroborated by the microstructural study of calcite mechanical twinning field relationships are used to establish the relative chronology of fractures and to deduce the motion on regional faults the reconstructed structural and tectonic evolution brings to light some relationships between structural inheritance and tectonic events that have affected the area since early palaeozoic times an early nw se extension is responsible for n040 trending faults along the northern border of the st lawrence lowlands and for n090 and n120 trending faults cross cutting the montreal area this extension is followed by wnw ese and nnw compressions which have induced reverse motion on pre existing faults and generated strike slip conjugate faults subsequent ne sw and nnw sse directed extensions have reactivated previous faults with normal to strike slip motions a late ne sw compression is recorded in the monteregian plutons compressions in wnw ese and nnw directions are consistent with appalachian collisional tectonism but n040 and n090 trending faults cross cut appalachian folds and foreland deposits although the early nw se extension is consistent with the collapse of the iapetan margin in early palaeozoic times most of the present geometry of the st lawrence lowlands could be attributed to mesozoic tectonism recorded as nearly n s directed extensional events

granites of western karakorum and northern kohistan pakistan a composite mid cretaceous to upper cenozoic magmatism abstract the petrography the chemical mineralogical typology and the ages of six plutonic units four from the karakorum axial batholith darkot pass ghamu bar batura and hunza units and two of northern kohistan gindai and nomal plutons are defined and compared based on field data and analyses of up to 78 samples major elements ree rb s sbnd sr and k ar isotopes the karakorum axial batholith is a composite body three major intrusive stages occurred 1 around mid cretaceous times ca 110 95 ma with the emplacement of subalkaline i e monzonitic darkot pass and calc alkaline hunza ghamu bar units 2 during palaeogene maybe up to 43 ma batura subalkaline unit a strong tectonommetamorphic event recorded in the gneissification of the cretaceous intrusives occurred between these two stages it may be of palaeocene age p t estimates of the highest metamorphic grade rocks of the hunza unit have yielded values of 580 640 c and 5 0 5 kbar and 3 during upper miocene ca 9 ma baltoro subalkaline unit debon et al 1986c in addition a conspicuous network of aplo pegmatitic dykes emplaced into the hunza area possibly from the eocene up to the upper cenozoic with a maximum during the middle miocene ca 15 ma most of these major magmatic stages are met again among the acidic intrusives and dykes of northern kohistan the first one as blastomylonitic tholeiitic plutons nomal ca 102 ma petterson and windley 1985 the second one as subalkaline plutons gindai ca 59 ma and a third one as leucocratic dykes of oligocene age ca 30 ma petterson and windley 1985 these data may be related to the geodynamic evolution of the nw part of the india eurasia suture zone thus allowing better constraints on the major steps of this evolution the partly synchronous closures by n dipping subduction of the two tethys branches which are assumed to have encircled the kohistan arc in upper mesozoic times may have generated both the karakorum and the kohistan intrusives of cretaceous and palaeogene ages the northern branch very likely closed before the southern one at the time of the second intrusive stage palaeogene a kohistan and karakorum had already collided were welded and had suffered the same major tectonometamorphic event b subduction of the southern tethys floor beneath the welded kohistan karakorum was still active c however collision between india and kohistan karakorum may have already begun particularly at the level of the nanga parbat promontory finally it is emphasized that the intrusive processes continued in the karakorum long after the collision e g baltoro granite

paleostress regimes from brittle structures of the karakoram kohistan suture zone and surrounding areas of nw pakistan paleostress orientations were calculated from fault populations at 24 sites along the sw ne segment and five sites along the e w yasin segment of the karakoram kohistan suture zone in nw pakistan they demonstrate the importance of combined thrusting and strike slip faulting however several paleostress tensor directions are distinguished a dominant nw se compression and a minor e w compression are compatible with the recent evolution of this part of the hindu kush from the lack of both systematic overprinting relationships and spatial trend the two tensors were obtained at different locations we conclude that in each location any of these two shortening directions can dominate heterogeneously distributed extension is found in some places and is likely due to local conditions these paleostress tensors substantiate a transpressional regime due to far field himalayan compression and document the long term background of the seismogenic deformation in this region

topographic effects on a wintertime cold front in taiwan abstract this paper describes an observational and numerical study of an intense wintertime cold front that occurred in taiwan on 8 january 1996 the front was associated with rope clouds at the leading edge and a broad area of stratiform clouds behind the front was blocked by the central mountain range of taiwan and divided into two sections on each side of the mountain range as the cold air moved southward along the east coast the increasing westward coriolis force induced a landward acceleration after the cold air piled up against the mountains a coastal pressure ridge developed the cold air damming yielded a geostrophic balance between the westward coriolis force and the eastward component of the pressure gradient force in the x direction and a southward acceleration in the y direction mainly caused by the southward pressure gradient force component over the taiwan strait southward pressure gradient forces increased when the low level stable cold air was confined over the taiwan strait lead

structural and thermal evolution of the karakoram crust prior to the eocene c 50 ma collision of the indian and asian plates the southern margin of asia along the karakoram plate was an andean type margin dominated by tonalitic granodioritic magmatism of jurassic lower cretaceous age hushe gneiss muztagh tower gneiss and k2 ortho gneiss and associated low pressure andalusite staurolite and garnet grade metamorphism m1 following india asia collision crustal shortening thickening and regional barrovian metamorphism m2 occurred between 50 37 ma thermobarometry of kyanite grade metapelites indicate burial to depths of around 30 35 km simultaneous solution of the garnet biotite geothermometer with the garnet muscovite biotite plagioclase and garnet ai 2 sio 5 quartz plagioclase geobarometers indicates peak m2 p t conditions of 696 20 c at 8 6 0 7kbar 860 mpa temperatures may have exceeded 700 c in sillimanite grade metapelites to produce in situ partial melting and leucogranitic melt pods peak m2 metamorphism occurred prior to 37 0 8 ma the crystallization age of the mango gusar two mica granite pluton which cross cuts syn metamorphic deformation fabrics post m2 thermal relaxation followed from 37 25 ma after which localized high heat concentrations at the base of the thickened crust caused widespread crustal melting and intrusion of the baltoro granite batholith at 25 21 ma a high temperature low pressure thermal aureole m3 along the northern contact is synchronous with the 21 0 5 ma zircon age of the baltoro granite andalusite hornfels along the northern contact of the batholith mitre thermal aureole indicates maximum pressures of 3 75 kbar 375 mpa a 75 c increase of temperature in kyanite sillimanite grade gneisses approaching the southern granite contact of the baltoro granite is interpreted as the thermal upwarping of pre 37 ma barrovian metamorphic m2 isograds around the 21 ma contact aureole m3 isotherms

multistage structural evolution of northern karakorum hunza region pakistan abstract detailed mapping and structural work in upper hunza valley pakistan have enlightened the tectonics and the structural evolution of the sedimentary cover of northern karakorum this includes the northern sedimentary belt nsb with the guhjal and sost units permian cretaceous cropping out north of the karakorum axial batholith kab the nsb is bounded to the north by the misgar unit consisting of slates of unknown age in the sost unit a mid cretaceous deformed belt is sealed with a strong angular unconformity by the late cretaceous formations folds within the mid cretaceous belt possibly indicate north vergent transport stacking of ne to n vergent thrusts sheets postdates the deposition of cretaceous sediments which are largely included within tectonic slices developed along the southern flank of the sost stack the southern part of the stack is in turn intruded by the palaeogene kuk pluton belonging to the batura unit of the kab s to sse vergent thrusting was successively active stacking steep north dipping thrust sheets along the northern side of the sost unit forming a complex antiformal stack well exposed around sost high angle pure dip slip reverse and oblique dextral motions are recorded by fault slip data and calc mylonites along major faults forming a transpressive fault zone close to the contact between the sost and misgar units during this stage the misgar unit was thrusted southward above the sost unit along the northern fault prosecution of dextral motion was also active afterwards along the boundary between the two units the importance of wrench tectonics is also indicated by widespread activation of e w sinistral strike slip faults in the whole study area generally moving along pre existent fault planes

seabed classification from acoustic profiling data using the similarity index we introduce the similarity index si for the classification of the sea floor from acoustic profiling data the essential part of our approach is the singular value decomposition of the data to extract a signal coherent trace to trace using the karhunen loeve transform si is defined as the percentage of the energy of the coherent part contained in the bottom return signals important aspects of si are that it is easily computed and that it represents the textural roughness of the sea floor as a function of grain size hardness and a degree of sediment sorting in a real data example we classified a section of the sea floor off cheju island south of the korean peninsula and compared the result with the sedimentology defined from direct sediment sampling and side scan sonar records the comparison shows that si can efficiently discriminate the bottom properties by delineating sediment type boundaries and transition zones in more detail therefore we propose that si is an effective parameter for geoacoustic modeling

evidence for the long term sedimentary environment in an antarctic subglacial lake lakes beneath the antarctic ice sheet are of fundamental scientific interest for their ability to contain unique records of ice sheet history and microbial life in their sediments however no records of subglacial lake sedimentation have yet been acquired from beneath the interior of the ice sheet and understanding of sediment pathways processes and structure in subglacial lake environments remains uncertain here we present an analysis of seismic data from subglacial lake ellsworth showing that the lake bed comprises very fine grained sediments deposited in a low energy environment with low water and sediment fluxes minimum sediment thickness is 6 m the result of prolonged low sedimentation rates based on the few available analogues we speculate this sediment age range is a minimum of 150 ka and possibly 1 ma sediment mass movements have occurred but they are rare and have been buried by subsequent sedimentation we present a new conceptual model of subglacial lake sedimentation allowing a framework for evaluating processes in subglacial lake environments and for determining future lake access locations and interpreting subglacial lake samples

marine sediment classification using the chirp sonar the chirp sonar is a calibrated wideband digital fm sonar that provides quantitative high resolution low noise subbottom data in addition it generates an acoustic pulse with special frequency domain weighting that provides nearly constant resolution with depth the chirp sonar was developed with the objective of remote acoustic classification of seafloor sediments in addition to producing high resolution images the calibrated digitally recorded data are processed to estimate surficial reflection coefficients as well as a complete sediment acoustic impulse profile in this paper surficial sediments in narragansett bay ri are used to provide ground truth for an acoustic model quantitative acoustic returns from the chirp sonar are used to estimate surficial acoustic impedance and to predict sediment properties a robust acoustic sediment classification model that uses core samples to account for the local depositional environment has been developed the model uses an estimate of acoustic impedance t

chirp subbottom profiler for quantitative sediment analysis a wide band frequency modulated subbottom profiling system the chirp sonar can remotely determine the acoustic attenuation of ocean sediments and produce artifact free sediment profiles in real time the chirp sonar is controlled by a minicomputer which performs analog to digital and digital to analog conversion correlation processing and attenuation estimation in real time the minicomputer generates an fm pulse that is phase and amplitude compensated to correct for the sonar system response such precise waveform control helps suppress correlation noise and source ringing the chirp sonar which has an effective bandwidth of 5 khz can generate chirp klauder wavelets with a tuning thickness rayleigh s criterion for resolution of approximately 0 1 ms after each return is correlated a computationally fast algorithm estimates the attenuation of subbottom reflections by waveform matching with a theoretically attenuated waveform this algorithm obtains an attenuation estimate by minimizing the m

field relationships and geochemistry of pre collisional india asia granitoid magmatism in the central karakoram northern pakistan in the central karakoram range northern pakistan seven major granitic units which were emplaced prior to the eocene ca 50 ma india asia collision have been mapped and analysed geochemically the mid cretaceous hunza plutonic complex dominates the karakoram batholith in the west and is composed of quartz diorite granodiorite plutons which have been deformed in the south by later collision related thrusting the sost and khunjerab plutons intrude the palaeozoic early mesozoic sediments north of the batholith in the east pre collision magmatic units occur both north of k2 gneiss broad peak quartz diorite muztagh tower unit and south of hushe gneiss the batholith which is dominated by a miocene monzogranite leucogranite pluton baltoro unit the plutonic units to the north of the batholith are mid to late cretaceous with an age range of ca 115 80 ma whereas the hushe gneiss to the south is dominantly jurassic spanning the age range 200 145 ma all the pre collision magmatic units display similar chemical and isotopic characteristics major trace and ree variations in the hunza plutonic complex are controlled by high level fractionation of clinopyroxene hornblende plagioclase biotite ilmenite and allanite high lile hfse and lree hree ratios together with negative nb p and ti anomalies suggest an ultimate source in the mantle wedge above the subducting slab 87sr 86sr initial ratios 0 7055 0 7157 in the hunza plutonic complex can best be explained by contamination of a mantle derived magma by a crustal component with highly radiogenic sr all the units except the hushe gneiss are probably related to subduction during closure of a back arc basin between the karakoram to the north and the kohistan dras arc to the south during the mid to late cretaceous and correlate with widespread plutonism from the same period in kohistan ladakh and southern tibet along the southern margin of asia the hushe gneiss is probably related to an earlier northward directed subduction phase during the jurassic