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

isotopic constraints on the structural relationships between the lesser himalayan series and the high himalayan crystalline series garhwal himalaya nd and sr isotope systematics may provide important constraints on the location of major thrust systems that separate lithologically similar sedimentary sequences the potential of the technique is illustrated by this isotopic study of the main central thrust system of the himalaya nd isotope data from the garhwal himalaya indicate that metasedimentary rocks from the vaikrita group nd 14 to 19 correlate closely with those from the high himalayan crystalline series which constitutes the hanging wall lithologies of the main central thrust in contrast metasedimentary rocks from the munsiari group nd 23 to 28 show marked similarities to the lesser himalayan series in the footwall of the main central thrust sr isotopes support the correlations in that the vaikrita group shows partial reequilibration at 500 ma whereas the munsiari group has not undergone sr isotope homogenization since 1800 ma thus the vaikrita thrust that juxtaposes these two formations is recognized as the main central thrust in garhwal himalaya the thrust coincides approximately with the location of the kyanite isograd confirming that inverted metamorphism is characteristic of both hanging wall and footwall of the main central thrust along the tons thrust known locally as the srinagar thrust 50 km south of the main central thrust low grade quartzarenites with nd sr isotope and trace element characteristics typical of lesser himalayan formations have been emplaced on phyllites and siltstones with geochemical characteristics of the high himalayan crystalline series the field relationships most probably result from out of sequence thrusting in which lesser himalayan series rocks to the north were emplaced over low grade equivalents of the high himalayan crystalline series preserved in the external part of the orogen this study establishes the value of isotope data for lithostratigraphic correlations within orogenic belts

zircon hf isotopic constraints on the sources of the indus molasse ladakh himalaya india 1 india asia collision has resulted in the largest orogenic event on earth since at least 500 ma and this has had a profound influence on the drainage patterns of asia on the asian monsoon climate on global oceanography as well as on faunal extinctions despite this importance understanding of the paleogene evolution of this system is limited u pb and lu hf isotopic analyses of detrital zircons from the clastic sedimentary rocks of the indus molasse located within the indus suture of the ladakh himalaya india show that most have mesozoic cenozoic ages and juvenile hf isotopic compositions this suggests that the main source of these sediments is the transhimalayan batholith with minor flux from the lhasa karakoram terrane and indian plate the lower indus molasse chogdo formation is inferred to have been deposited at 60 49 ma whereas the upper choksti formation was deposited later than 45 41 ma and contains a greater contribution from the lhasa terrane the transhimalayan batholith was eroded throughout indus molasse sedimentation but increasing exhumation of lhasa karakoram terrane indicates its progressive uplift after initial collision and requires formation of apaleo indus river shortly after collision

oxygen isotopic compositions of allende type c cais evidence for isotopic exchange during nebular melting and asteroidal metamorphism abstract in situ oxygen isotopic measurements of primary and secondary minerals in type c cais from the allende cv3 chondrite reveal that the pattern of relative enrichments and depletions of 16 o in the primary minerals within each individual cai are similar to the patterns observed in types a and b cais from the same meteorite spinel is consistently the most 16 o rich 17 o 25 to 15 followed by al ti dioside 17 o 20 to 5 and anorthite 17 o 15 to 0 melilite is the most 16 o depleted primary mineral 17 o 5 to 3 we conclude that the original melting event that formed type c cais occurred in a 16 o rich 17 o 20 nebular gas and they subsequently experienced oxygen isotopic exchange in a 16 o poor reservoir at least three of these abc ts26f1 and 93 experienced remelting at the time and place where chondrules were forming trapping and partially assimilating 16 o poor chondrule fragments the observation that the pyroxene is 16 o rich relative to the feldspar even though the feldspar preceded it in the igneous crystallization sequence disproves the class of cai isotopic exchange models in which partial melting of a 16 o rich solid in a 16 o poor gas is followed by slow crystallization in that gas for the typical not associated with chondrule materials type c cais as well for as the types a and b cais the exchange that produced internal isotopic heterogeneity within each cai must have occurred largely in the solid state the secondary phases grossular monticellite and forsterite commonly have similar oxygen isotopic compositions to the melilite and anorthite they replace but in one case cai 160 grossular is 16 o enriched 17 o 10 to 6 relative to melilite 17 o 5 to 3 meaning that the melilite and anorthite must have exchanged its oxygen subsequent to secondary alteration this isotopic exchange in melilite and anorthite likely occurred on the cv parent asteroid possibly during fluid assisted thermal metamorphism

tibetan tectonic evolution inferred from spatial and temporal variations in post collisional magmatism cenozoic magmatism on the tibetan plateau shows systematic variations in space and time that must be considered in models concerning tibetan tectonic evolution after the india asia collision which started in the early tertiary and terminated the gangdese arc magmatism in the lhasa terrane made of the southern tibetan plateau widespread potassium rich lavas and subordinate sodium rich basalts were generated from f50 to 30 ma in the qiangtang terrane of northern tibet subsequent post collisional magmatism migrated southwards producing ultrapotassic and adakitic lavas coevally between f26 and 10 ma in the lhasa terrane then potassic volcanism was renewed to the north and has become extensive and semicontinuous since f13 ma in the western qiangtang and songpan ganze terranes such spatial temporal variations enable us to elaborate a geodynamic evolution model which depicts when and how the indian continental lithospheric mantle started thrusting under asia by involving rollback and breakoff of the subducted neo tethyan slab followed by removal of the thickened lhasa lithospheric root we propose that only after the lithospheric removal which occurred at f26 ma could the indian mantle lithosphere have commenced its northward underthrusting and henceforth served as a pivotal control to the himalayan tibetan orogenesis consequently the tibetan plateau is suggested to have risen diachronously from south to north whereas the southern part of the plateau may have been created and maintained since the late oligocene the northern plateau would have not attained its present day elevation and size until the mid miocene when the lower part of the western qiangtang and songpan ganze lithospheres began to founder owing to the push of the underthrust indian mantle lithosphere d 2004 elsevier b v all rights reserved

testing the application of in situ sm nd isotopic analysis on detrital apatites a provenance tool for constraining the timing of india eurasia collision provenance tools are applicable to many problems in sedimentary geology as they help unravel the tectonic and metamorphic history of the hinterland and provide insights into the erosional pathways and origins of sediments in many cases it is more appropriate to use single grain approaches as opposed to bulk sediment methods in order to discover the precise input of the contributing geological terranes since the input of subordinate sources may not be detectable in bulk rock studies using a selection of modern river sediments we characterise the sm nd isotopic composition of individual detrital apatites from the main himalayan geological terranes our analyses allow us to effectively distinguish between apatites derived from the eurasian plate relatively high end values and low 147sm 144nd ratios from those derived from the indian plate low to high end values and moderate to high 147sm 144nd ratios we then apply this approach to tertiary indus basin sedimentary rocks to attempt to better determine the timing of india eurasia collision we find that detrital apatites in the tertiary indus basin have been sourced solely from eurasia lacking a mixed india eurasia provenance input which would document the india eurasia collision this study illustrates the use of this relatively novel provenance tool and provides a sound framework for similar studies in the future concerning the tectono metamorphic erosional evolution of the himalaya

sr isotope evolution of seawater the role of tectonics we use a high resolution seawater sr isotopic evolution curve for the last 100 m y in conjunction with modern riverine sr flux measurements and also geologic tectonic and geochronological data to make the case for a close relationship between seawater sr isotopic composition and the india asia continental collision using a simple seawater sr budget model we begin by showing that the sr flux associated with alteration of seafloor basalts is too small and does not have the right time evolution to account for much of the seawater sr isotopic curve of the last 100 m y the flux of dissolved sr carried by rivers originating in the himalaya tibet region on the other hand is presently a significant fraction of the global sr budget we calculate how this riverine flux would have had to change with time in order to match the observed seawater sr isotopic curve and find that the riverine flux remains relatively constant prior to the collision of india with asia but then increases very significantly after collision we note that the period of most rapid change in seawater sr isotopic ratio from 20 ma to 15 ma is also a period of exceptionally high erosion in parts of the himalayas and the tibetan plateau as further evidence that sr derived from the collision of india with asia plays a major role in the sr isotopic evolution of seawater we show that the total amount erosion of the himalaya tibetan plateau since collision which we calculate separately represents a total amount of sr that is very nearly the same as the cumulative amount required by the sr isotopic change of seawater since collision the relationship between erosion and riverine sr flux allows us to use the sr isotopic evolution of seawater to reconstruct a history of erosion since collision and we find that the erosion rate accelerates with time since collision with the present having the largest rate when we apply the sr budget model to the entire phanerozoic using a new compilation of deformed continental area versus time we find that we can account for the large scale structure of the seawater sr isotopic curve but fail to reproduce several local maxima and minima especially in the period 100 300 ma the present high s7sr s6sr of seawater and similar highs in the devonian and cambrian do correlate with extensive deformation on the continents

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

apatite triple dating and white mica 40ar 39ar thermochronology of syntectonic detritus in the central andes a multiphase tectonothermal history we applied apatite u pb fission track and u th he triple dating and white mica 40 ar 39 ar thermochronology to syntectonic sedimentary rocks from the central andean puna plateau in order to determine the source area geochronology and source sedimentary basin thermal histories and ultimately the timing of multiple tectonothermal events in the central andes apatite triple dating of samples from the eocene geste formation in the salar de pastos grandes basin shows late precambrian devonian apatite u pb crystallization ages eocene apatite fission track aft and eocene miocene u th he ca 8 47 ma cooling ages double dating of cobbles from equivalent strata in the arizaro basin documents early eocene 46 2 3 9 ma and cretaceous 107 6 7 6 109 5 7 7 ma aft and eocene oligocene ca 55 30 ma u th he ages thermal modeling suggests relatively rapid cooling between ca 80 and 50 ma and reheating and subsequent diachronous basin exhumation between ca 30 ma and 5 ma the 40 ar 39 ar white mica ages from the same samples in the salar de pastos grandes area are mainly 400 350 ma younger than apatite u pb ages suggesting source terrane cooling and exhumation during the devonian early carboniferous together these data reveal multiple phases of mountain building in the paleozoic and cenozoic basin burial temperatures within the plateau were limited to

the onset of india asia continental collision early steep subduction required by the timing of uhp metamorphism in the western himalaya ultrahigh pressure uhp rocks in the nw himalaya are some of the youngest on earth and allow testing of critical questions of uhp formation and exhumation and the timing of the india asia collision initial collision of india with asia is widely cited as being at 55f1 ma based on a paleomagnetically determined slowdown of india s plate velocity and as being at ca 51 ma based on the termination of marine carbonate deposition even relatively small changes in this collision age force large changes in tectonic reconstructions because of the rapid india asia convergence rate of 134 mm a at the time of collision new u pb shrimp dating of zircon shows that indian rocks of the tso morari complex reached uhp depths at 53 3f0 7 ma given the high rate of indian subduction this dating implies that indian continental crust arrived at the asian trench no later than 57f1 ma providing a metamorphic age for comparison with previous paleomagnetic and stratigraphic estimates india s collision with asia may be compared to modern processes in the timor region in which initiation of collision precedes both the slowing of the convergence rate and the termination of marine carbonate deposition the indian uhp rocks must have traveled rapidly along a short hence steep path into the mantle early continental subduction was at a steep angle probably vertical comparable to modern continental subduction in the hindu kush despite evidence for modern day low angle subduction of india beneath tibet oceanic slab break off likely coincided with exhumation of uhp terranes in the western himalaya and led to the initiation of low angle subduction and leucogranite generation d 2005 elsevier b v all rights reserved

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

constraints to the timing of india eurasia collision a re evaluation of evidence from the indus basin sedimentary rocks of the indus tsangpo suture zone ladakh india deposited within the indus tsangpo suture zone the cenozoic indus basin sedimentary rocks have been interpreted to hold evidence that may constrain the timing of india eurasia collision a conclusion challenged by data presented here the eurasian derived 50 8 51 ma chogdo formation was previously considered to overlie indian plate marine sedimentary rocks in sedimentary contact thus constraining the timing of collision as having occurred by this time using isotopic analysis u pb dating on detrital zircons ar ar dating on detrital white mica sm nd analyses on detrital apatite sandstone and conglomerate petrography mudstone geochemistry facies analysis and geological mapping to characterize and correlate the formations of the indus basin sedimentary rocks we review the nature of these contacts and the identification and correlation of the formations our results reveal that previously interpreted stratigraphic contacts identifying chogdo formation unconformably overlying indian plate sedimentary rocks are incorrect rather we suggest that the inaccuracy of previous interpretations is most likely a result of formation misidentification and thus cannot be used to constrain the timing of india asia collision

isotopic constraints on the age and provenance of the lesser and greater himalayan sequences nepalese himalaya the main central thrust of the central himalaya juxtaposes the lesser himalayan sequence footwall with the greater himalayan sequence hanging wall both of which are regarded as components of the northern passive margin of india considerable uncertainty surrounds their respective ages and sedimentary derivation u pb and sm nd isotopic studies of samples from the langtang area central nepal demonstrate important distinctions between the two rock packages the greater himalayan sequence had a sedimentary provenance that included a major source of 0 8 1 0 ga zircons implying a late proterozoic age the source of the precambrian part of the lesser himalayan sequence contained 1 87 2 60 ga zircons and its depositional age is probably middle proterozoic nd isotopic characteristics of the two sequences are different at 21 ma the greater himalayan rocks had end values between 14 6 and 18 5 while their lesser himalayan counterparts had values between 21 4 and 25 9 giving rise to major differences in their model ages the lesser and greater himalayan sequences at langtang are interpreted as correlative to the lower and upper parts of the vindhyan supergroup currently exposed south of the gangetic plain in northern india on the basis of available age data the exposed hanging wall of the main central thrust in central and eastern nepal contains no archean early proterozoic basement if the fault does root into the basement at depth it must do so farther north than recently published cross sections indicate this implies a total displacement on the fault that is substantially greater than the 140 210 km required by tectonic overlap in the eastern himalayas

proterozoic crustal evolution in the nw himalaya india as recorded by circa 1 80 ga mafic and 1 84 ga granitic magmatism abstract single zircon dating of the rampur metabasalts of the larji kullu rampur window in the lesser himalayas yielded an evaporation age of 1800 13 ma the zircon age is considerably younger than the previously published whole rock sm nd age of 2510 90 ma suggesting that the sm nd age may be geologically meaningless and that the sm nd whole rock array may have resulted from mixing in the nw himalaya there is also evidence for extensive silicic melt generation in the paleoproterozoic zircons from a metarhyodacite in the larji kullu rampur window yielded an evaporation age of 1840 16 ma which we interpret as the minimum age of magmatism the main central thrust granitic mylonites are interpreted as the basement of the neoproterozoic haimanta group metasediments together with the granitic rocks from the lesser himalaya they were derived from pre existing continental crust prior to 1 84 ga the nd depleted mantle model ages are in the range of 2 6 2 4 ga suggesting a contribution of archean crust a recycled archean component is also documented by a 2 9 ga domain in one of the zircons

cretaceous tertiary carbonate platform evolution and the age of the india asia collision along the ladakh himalaya northwest india abstract the india asia collision resulted in the formation and uplift of the himalaya and the enhanced uplift of the tibetan plateau the transition from marine to continental facies within the indus yarlung tsangpo suture zone and along the northern margin of the indian plate provides the most accurate method of dating the closure of the tethys ocean separating the indian and asian plates other indirect methods of dating the collision such as paleomagnetism dating the uhp metamorphism along the north margin of india dating the youngest subduction related granites along the southern margin of asia and dating the postorogenic indus molasse group deposits within the suture zone cannot provide such a precise or reliable age of collision ophiolite obduction onto the indian passive margin occurred during the latest cretaceous and predated initial collision of the two continental plates unconformities occur beneath the late maastrichtian marpo formation and beneath the danian stumpata formation on the

the indus clastics forearc basin sedimentation in the ladakh himalaya india abstract the mid cretaceous to early tertiary clastic sediments of the indus group represent the forearc basin succession of the transhimalayan arc trench system in the late albian to early eocene a shallowing upward megasequence tar turbidites to nummulitic limestones and alluvial to deltaic sediments basgo and temesgam formations were deposited respectively on the southern and northern flanks of the basin clastic petrography points to provenance from the largely undissected volcanic cover of the massif with more important plutonic detritus recorded in the northern alluvial units after collision with the indian passive margin in the early eocene sedimentation in the whole basin was characterized by huge alluvial fans nurla formation and then by lacustrine deposits formed in an intermontane depression nimu formation a rapid change in petrographic and geochemical composition is recorded in post early eocene units with sharp increase in plutonic detritus and trace elements typically associated with ophiolites testifying to the uplift of both arc massif and subduction complex sources after collision with the indian passive margin the petrography of the indus basin clastics and the evolution of detrital modes compare well with volcano plutonic suites deposited in modern and ancient forearc basins the composition of sandstone units contained within the accretionary prism instead suggests provenance from an undissected magmatic arc and deposition in abyssal plain and trench settings nindam volcaniclastic turbidites reworking of arc derived sandstones took place in small basins perched on the accretionary trench slope the asian continental margin of the neotethys ocean was thus an active pacific type arc trench system until the eocene when it collided with india underwent polyphase fold thrust deformation and was finally uplifted several kilometers to form the indus suture zone of the himalayas

tracing patterns of erosion and drainage in the paleogene himalaya through ion probe pb isotope analysis of detrital k feldspars in the indus molasse india abstract the indus molasse is a pre and syn tectonic sedimentary sequence situated in the indus suture zone of the western himalaya spanning in time the collision of india and asia this deposit is well placed to record the evolving uplift and erosion history of the early himalayan orogen nd isotope analyses from clay extracted from shales interbedded within the dominantly alluvial sequence indicate a low negative nd 1 64 to 0 72 in the basal paleocene chogdo formation slightly more negative than measured values from the transhimalaya and kohistan dras arc up section nd becomes more negative as low as 10 05 indicating influence of a different more enriched source ion microprobe pb isotopic analyses of single k feldspars help constrain this source as being either the lhasa or karakoram blocks with westward paleo current flow favoring the former 207pb 204pb ratios are too low to be consistent with known indian plate sources a conclusion supported by the lack of muscovite or garnet that would be indicative of a high himalayan contribution given the known age of rapid cooling of the high himalaya at 20 ma and the lack of exposure of suitable lithologies prior to that time an age of sedimentation prior to 20 ma is inferred the post collisional change in paleo flow and provenance is suggested to reflect the initiation of the indus river during the early eocene this study demonstrates the power of combined bulk sediment and single grain analyses in resolving provenance in tectonically complex settings

the kinematic evolution of the nepalese himalaya interpreted from nd isotopes neodymium nd isotopes from the himalayan fold thrust belt and its associated foreland basin deposits are useful for distinguishing between himalayan tectonostratigraphic zones and revealing the erosional unroofing history as controlled by the kinematic development of the orogen neodymium isotopic data from the himalayan fold thrust belt in nepal n 35 reveal that the lesser himalayan zone consistently has a more negative nd 0 value than the greater and tibetan himalayan zones our data show the average nd 0 value in the lesser himalayan zone is 21 5 whereas the greater and tibetan himalayan zones have an average nd 0 value of 16 these consistently distinct values throughout nepal enable the use of nd isotopes as a technique for distinguishing between lesser himalayan zone and greater himalayan zone rock the less negative nd 0 values of the greater himalayan rocks support the idea that the greater himalayan zone is not indian basement but rather a terrane that accreted onto india during early paleozoic time neodymium isotopic data from eocene through pliocene foreland basin deposits n 34 show that sediment provenance has been dominated by greater and tibetan himalayan detritus across nepal the nd t values in the synorogenic rocks in western and central nepal generally show an up section shift toward more negative values and record the progressive unroofing of the different tectonostratigraphic zones at 10 ma in khutia khola and 11 ma in surai khola a shift in nd t values from 16 to 18 marks the erosional breaching of a large duplex in the northern part of the lesser himalayan zone this shift is not seen in eastern nepal where the nd t values remain close to 16 throughout miocene time because there has been less erosional unroofing in this region

himalayan architecture constrained by isotopic tracers from clastic sediments we report the first geochemical traverse to integrate u pb ages and hf data on single detrital zircons with bulk rock sm nd rb sr isotopic measurements across the breadth of the himalayan orogen in northwest india our dataset from key tectonostratigraphic units in the sutlej valley provides detailed insights into both the provenance of the sedimentary formations and their tectonic history whole rock nd data provide information on the mean age of source areas contributing detritus to the sedimentary units in the mountain belt regardless of their current metamorphic grade u pb ages of detrital zircons from the same units identify the age of melt formation in the source rocks while lu hf isotope data from zircons resolve discrete crust formation ages in the multiple eroding terrains complex whole rock sr systematics hint at the extent of pre himalayan thermal events our data confirm the geochemical distinction between the older lesser himalayan formations and those of the depositionally younger units including the high himalayan crystalline series that has been recorded along the strike of the himalaya from the western syntaxis to nepal palaeoproterozoic metasediments of the jutogh group and rampur formation yield end 500 values below 17 whereas neoproterozoic and younger metasediments yield end 500 above 13 the latter group encompasses the vaikrita group gneisses of the high himalayan crystallines and the overlying haimanta group but also includes a number of units in thrust sheets north of the main boundary thrust in the lesser himalayan zone designated the douter lesser himalayat to distinguish them from the palaeoproterozoic dinner lesser himalayat zircon populations from the inner lesser himalaya are characterised by palaeoproterozoic late archaean ages 2 6 1 8 ga whereas the depositionally younger units contain populations both of this age and a younger period meso to neo proterozoic 1 1 0 8 ga detrital zircon ages are younger than their respective hf isotope derived crustal formation ages by 0 7 2 1 ga indicating that the source regions of the detrital zircons consisted of older terranes with considerable amounts of reworking and renewed magmatism the

multicyclic history of the northern india continental margin northwestern himalaya 1 the geologic evolution of northern india is best recorded in the stratigraphic succession of the zanskar range northwestern himalaya which represents the most complete transect through this ancient continental margin sedimentary history began in the late proterozoic and recorded a late pan african orogenic event around the cambrian ordovician boundary when the gondwana supercontinent was eventually assembled the following long period of epicontinental deposition in shallow seas linked to palaeo tethys lasted until the early permian when a neo tethyan rift began to open between paleo india and the cimmerian microcontinents neo tethyan history can be subdivided into two sedimentary megasequences both recording a major tectonic and magmatic event in the lower part the first one began with breakup in the late permian and lasted until the end of the jurassic the second one started in the early cretaceous with the final detachment of india from gondwana and the opening of the indian ocean and ended with the india eurasia collision in the early eocene the two megasequences can be in turn subdivided into six transgressive regressive supersequences bounded by tectonically enhanced unconformities basal sandstone units of early permian late permian norian callovian early cretaceous and paleocene age are invariably associated with oolitic ironstones or reworked glauco phosphorites and mark the transgre sive part of each supersequence next condensed nodular carbonates or shales with pelagic fauna are typically overlain by thick shallowing upward marly units capped by regressive platformal carbonates the six tectono eustatic supercycles reflect successive rifting episodes which punctuated the progressive separation of india from the rest of gondwana and document the combination of plate microplate reorganizations and eustatic climatic and oceanographic changes in the tethyan domain after the onset of collision between india and asia close to the paleocene eocene boundary obduction of the remnants of the neo tethys ocean floor onto the indian margin began and the latter underwent multiphase deformation with fold thrust shortening followed by heating and extension after the main metamorphic event ophiolitic nappes were re thrusted and finally emplaced with their sedimentary sole on top of the passive margin succession

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

age cooling history and origin of post collisional leucogranites in the karakoram batholith a multi system isotope study u pb dating on zircon and monazite from different varieties of leucogranites in the karakoram batholith reveals two distinct pulses of plutonism at 25 5 0 3 0 8 and 21 4 0 3 0 6 ma in both granites these minerals contain inherited components documenting the presence of precambrian material in the magma source a crustal origin of the granites and long crustal residence times of the source rocks are confirmed by highly negative epsilon i nd strongly positive epsilon i sr and t dm nd in excess to 1 ga a biotite gneiss and a granitic dike from the karakoram metamorphic complex south of the batholith yield very similar epsilon i nd epsilon i sr t dm nd in a pb evolution diagram initial isotopic compositions for both the granites and the rocks from the metamorphic complex plot far above the reference field for morb documenting very close affinity to the eurasian tibetan continental crust the striking similarity of isotope signatures between leuco

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

geology of the cenozoic indus basin sedimentary rocks paleoenvironmental interpretation of sedimentation from the western himalaya during the early phases of india eurasia collision this study reassesses the stratigraphy sedimentology and provenance of the indus basin sedimentary rocks deposited within the indus tsangpo suture zone itsz during the early phases of india eurasia collision using field observations biostratigraphy and petrographic and isotopic analyses we create a paleodepositional reconstruction within the paleotectonic setting of the early phases of india eurasia collision we then re examine existing constraints to the timing of india eurasia collision previously interpreted from the earliest occurrence of mixed indian and eurasian derived detritus in the succession from mid cretaceous to early paleocene times the jurutze and sumda formations were deposited within an arc bounded marine basin between the dras and kohistan ladakh island arcs the 51 ma aged deltaic chogdo formation then filled the basin until deposition of the 50 8 49 4 ma aged nummulitic limestone during a marine incursion before continental facies developed in an evolving intermountain basin with the deposition of the paleogene indus group within these systems sediment was sourced from the eurasian margin to the north and was transported southward into the suture zone in this section we see no unequivocal evidence of indian plate input to the sedimentary succession and thus no evidence of mixed indian eurasian derived detritus indicative of india asia collision until the upper stratigraphic horizons of the indus group when facies are representative of an axial northwesterly flowing river system we suggest that the paleo indus river was initiated within the itsz during late oligocene early miocene times sedimentation of the indus group continued until the late miocene

upb geochronology of gangdese transhimalaya plutonism in the lhasa xigaze region tibet abstract a series of different plutons from the lhasa xigaze segment of the gangdese transhimalaya belt has been studied by high resolution u pb analyses of zircon using zircon fractions of 5 100 grains each selected upon specific grain characteristics for two diorites located east of xigaze dazhuka the zircons yield concordant ages of 93 4 1 0 and 94 2 1 0 m y respectively also concordant ages of 41 1 0 4 and 41 7 0 4 m y have been obtained for two granodiorites collected southwest of lhasa qushui the precision on the ages of two granites from the xigaze and lhasa area is limited by two factors the presence of inherited radiogenic lead and the occurrence of subsequent lead loss however some concordant zircons detected in both granites define approximate ages of about 67 and 53 m y respectively the inherited lead components show that melting of precambrian material was involved in magma genesis the u pb ages substantiate a magmatic activity lasting from mid cretceous cenomanian to eocene lutetian time such a period of plutonism at the southern margin of eurasia as well as the occurrence of magma generation from continental crust suggest that the gangdese range results from the subduction of tethys oceanic lithosphere indian plate underneath eurasia eurasian plate if this model is true the collision of india with eurasia along the lhasa xigaze sector postdates the emplacement of the 41 m y old gangdese granodiorites i e the collision occurred after lutetian time

paleogeographic and paleotectonic evolution of the himalayan range as reflected by detrital modes of tertiary sandstones and modern sands indus transect india and pakistan detrital modes of sandstones derived from the himalayan suture belt record the history of the mountain range since initial collision between india and asia which began in latest paleocene time tertiary clastic wedges deposited in fore arc foreland and remnant ocean basins and exposed along the indus transect from northernmost india to the arabian sea represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision quartzose continental block and feldspatholithic magmatic arc sandstones were deposited respectively on the passive indian tethys himalayan succession and active asian indus group continental margins during late cretaceous paleocene time closure of the neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the indian plate during deposition of sediments dated at foraminiferal zones p6 pakistan to p8 india starting in early eocene time deposition of chulung la formation and murree supergroup volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding piggy back and foreland basins homogeneous petrographic composition within the eocene lower miocene murree supergroup with only slight progressive increase of detrital feldspars suggests erosion of largely supracrustal rocks involved in thrusting in the north in middle miocene time marked enrichment in medium to high grade metamorphic detritus in foreland sandstones siwalik group reflects rapid uplift of a warm wedge of indian crust which was carried southward along the main central thrust this major paleogeographic change was recorded also by quartzolithic remnant ocean turbidites which were fed great distances along transverse fracture zones and later accreted in the coastal makran subduction complex panjgur association and makran group recycled orogen detritus derived from the elevated himalayan chain is still accumulating today in the indus fan enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid crustal rocks along the core of the growing orogen

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

lithostratigraphic correlations in the western himalaya an isotopic approach we present the results of a whole rock nd isotopic study of two contrasting regions of the western himalaya using the neodymium model age approach on the scale of a single orogen high grade metasedimentary rocks from zanskar yield model ages t dm that are similar to those of the high himalayan crystalline series t dm 1 2 2 0 ga nd 6 to 16 and distinct from values from the lesser himalaya t dm 2 3 3 4 ga nd 18 to 27 hence these two lithological sequences can be recognized for 2000 km along the strike of the orogen data for the basement of the nanga parbat massif at the western extremity of the himalaya t dm 2 3 2 8 ga nd 18 to 30 suggest that these rocks are not equivalent to the high himalaya as previously supposed but have affinities with the lesser himalaya a thin metasedimentary cover sequence on the margins of the nanga parbat massif is isotopically indistinguishable from the high himalaya t dm 1 6 1 8 ga nd 10 to 14 the prior misidentification of the provenance of the massif stems from its high metamorphic grade characteristic of the high himalaya but in this case related to the unique neogene history of the nanga parbat massif which has exhumed a higher grade equivalent of the lesser himalaya that is not seen elsewhere

propagation of the thrust system and erosion in the lesser himalaya geochemical and sedimentological evidence centre de recherches pe trographiques et ge ochimiques bp 20 54501 vandoeuvre les nancy franceabstractsedimentological and nd isotope data of two sections of the sub himalaya of westernnepal are used as new constraints for understanding the erosion history of the himalaya throughout the deposition of the middle and upper members of the siwalik group thelesser himalaya contribution to the total detrital input progressively increased from lessthan 20 to 40 the increasing proportion of lesser himalaya sediments started at ca 10 8 ma and is associated with a coarsening of the maximum grain size at both micro scopic and macroscopic scales thin skinned tectonics of the lesser himalaya thrust sys tem would have controlled the exhumation of the lesser himalaya rocks and would havebegun at 12 10 ma taking into account the delay for denudation together with otherstudies these data restrict the onset of movement on the lesser himalaya thrust systemto less than 3 m y along more than 1750 km this short time frame implies a ratio oflateral propagation rate to shortening rate far too high for the propagation of a singlecrustal thrust thus we suggest instead the simultaneous initiation of several thrusts aheadof the main central thrust at ca 12 ma we suggest that a rapid rise of the tibetanplateau at this time has transformed the himalaya to an overcritical thrust wedge thathas propagated forward to return to a stable state this regional rising could be the primecause of the increase of sediment in ux at ca 11 ma around the himalaya keywords siwalik formations neodymium grain size erosion thrust sheets himalaya

restoration and evolution of the intermontane indus molasse basin ladakh himalaya india abstract collision of the indian plate with the karakorum plate lhasa block during the eocene ca 55 50 ma created predominantly a s or sw verging thrust culmination across the himalaya during the late tertiary two molasse basins existed the siwalik bain formed in the late miocene to present on the indian foreland south of the himalaya and the mid eocene to late miocene indus basin along the indus suture zone north of the high himalaya the indus basin is approximately 2000 km long extending eastwards from ladakh across south tibet a balanced cross section along the zanskar river shows a minimum 36 km shortening in the eocene late miocene molasse and suggests that the minimum basin width was approximately 60 km in ladakh more than 2000 m of post eocene alluvial fan fluvial and fluvio lacustrine sediments accumulated in the ladakh sector with petrographies suggesting derivation mainly from the deeply dissected and uplifted northern granodioritic ladakh batholith aptian eocene with only minor amounts of debris derived from the deformed southern tethyan passive margin palaeocurrents show predominant e w axis parallel sediment transport with subordinate lateral input paths being preserved the indus molasse basin is deformed by numerous post eocene n directed backthrusts many of which cut the entire stratigraphy and therefore were active at least into late tertiary times

structural evolution and sequence of thrusting in the high himalayan tibetan tethys and indus suture zones of zanskar and ladakh western himalaya reply abstract the timing of motion on major thrusts in the western himalaya shows an extremely complex sequence that spans approximately 70 ma from the latest cretaceous throughout the tertiary three major phases of thrusting can be distinguished the earliest phase t1 is associated with emplacement of tethyan basin thrust sheets lamayuru sediments and spontang ophiolite south and south westwards onto the submerged northern passive margin of india 75 60 ma collision between india and asia occurred at 50 36 ma and was followed immediately by the major phase t2 of crustal shortening involving large scale south and south westward directed thrusting of the complete palaeozoic mesozoic and late tertiary tibetan tethys zone rocks preliminary balanced cross sections show a minimum shortening of 126 km of these rocks across the zanskar range the late collision phase t3 involved re thrusting of the previously stacked pile breaching or leap frog thrusting reversing the earlier stacking order in places and widespread steepening overturning and backthrusting along the whole northern margin of the tibetan tethys zone and throughout the indus suture zone

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

crude oil in a shallow sand and gravel aquifer ii organic geochemistry abstract crude oil spilled from a pipeline break in a remote area of north central minnesota has contaminated a shallow glacial outwash aquifer part of the oil was sprayed over a large area to the west of the pipeline and part of it accumulated in an oil body that floats at the water table to the east of the point of discharge total dissolved organic carbon tdoc concentrations in shallow groundwater collected in the oil spray area reach 16 mg l this is nearly an order of magnitude higher than the tdoc concentrations of native groundwater 2 3mg l the additional tdoc derives from the partial degradation of petroleum residues deposited at the land surface and transported to the aquifer by vertical recharge in the vicinity of the oil body tdoc concentrations in groundwater are 48 mg l 58 of the tdoc being composed of non volatile organic c the majority of the volatile doc 63 is a mixture of low molecular weight saturated aromatic and alicyclic hydrocarbons derived from the oil downgradient from the oil body along the direction of groundwater flow concentrations of all measured constituents of the tdoc pool decrease concentrations begin to decline most rapidly however in the zone where dissolved o 2 concentrations begin to increase 50m downgradient from the leading edge of the oil within the anoxic zone near the oil body removal rates of isometric monoaromatic hydrocarbons vary widely this indicates that the removal processes are mediated mainly by microbiological activity molecular and spectroscopic characterization of the tdoc and its spatial and temporal variation provide evidence of the importance of biogeochemical processes in attenuating petroleum contaminants in this perturbed subsurface environment

provenance of the tertiary sedimentary rocks of the indo burman ranges burma myanmar burman arc or himalayan derived the indo burman ranges in western myanmar extend along the sunda arc subduction zone and may be divided into a western portion of neogene sedimentary rocks and an eastern portion of palaeogene sedimentary rocks separated by the kaladan fault both himalayan and burman sources have been proposed for these sediments our thermochronological analyses on detrital grains isotopic analyses on bulk rock and petrographic and heavy mineral data indicate that the palaeogene indo burman ranges contain a significant component of arc derived material interpreted as derived from the burmese portion of the mesozoic tertiary arc to the east and older crustal component is also identifiable which may have been sourced from the himalaya or the burmese margin by contrast the neogene indo burman ranges show dominant derivation from the himalaya a minor arc derived component may have been sourced from the trans himalaya or recycled from the arc derived paleogene indo burman ranges

dating the indian continental subduction and collisional thickening in the northwest himalaya multichronology of the tso morari eclogites multichronometric studies of the low temperature eclogitic tso morari unit ladakh india place timing constraints on the early evolution of the northwest himalayan belt several isotopic systems have been used to date the eclogitization and the exhumation of the tso morari unit lu hf sm nd rb sr and ar ar a ca 55 ma age for the eclogitization has been obtained by lu hf on garnet omphacite and whole rock from mafic eclogite and by sm nd on garnet glaucophane and whole rock from high pressure metapelites these results agree with a previously reported u pb age on allanite and together these ages constrain the subduction of the indian continental margin at the paleocene eocene boundary during exhumation the tso morari rocks underwent thermal relaxation at about 9 3 kbar characterized by partial recrystallization under amphibolite facies conditions ca 47 ma as dated by sm nd on garnet calcic amphibole and whole rock from metabasalt rb sr on phengite apatite and whole rock and ar ar on medium si phengite from metapelites ar ar analyses of biotite and low si muscovite from metapelites which recrystallized at 5 kbar toward the end of the exhumation show that the tso morari unit was at upper crustal levels ca 30 ma these results indicate variable exhumation rates for the tso morari unit beginning with rapid exhumation while the indian margin subduction was still active and later proceeding at a slower pace during the crustal thickening associated with the himalayan collision

crude oil in a shallow sand and gravel aquifer iii biogeochemical reactions and mass balance modeling in anoxic groundwater abstract crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near bemidji minnesota the degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body the concentrations of fe2 mn2 and ch4 eh measurements and the 13c ratios of the total inorganic c indicate that the plume became more reducing ver a 5 a period however the size of the contaminant plume remained stable during this time field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment in anaerobic microcosm experiments conducted under field conditions almost complete degradation 98 was observed for benzene in 125 d and for toluene in 45 d concentrations of aqueous fe2 and mn2 increased in these experiments indicating that the primary reactions were hydrocarbon degradation coupled with fe and mn reduction mass transfer calculations on a 40 m flowpath in the anoxic zone downgradient from the oil body indicated that the primary reactions in the anoxic zone are oxidation of organic compounds precipitation of siderite and a ferroan calcite dissolution of iron oxide and outgassing of ch4 and co2 the major difference in the two models presented is the ratio of co2 and ch4 that outgasses both models indicate quantitatively that large amounts of fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume