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

the distribution of deformation in parallel fault related folds with migrating axial surfaces comparison between fault propagation and fault bend folding abstract in fault related folds that form by axial surface migration rocks undergo deformation as they pass through axial surfaces the distribution and intensity of deformation in these structures has been impacted by the history of axial surface migration upon fold initiation unique dip panels develop each with a characteristic deformation intensity depending on their history during fold growth rocks that pass through axial surfaces are transported between dip panels and accumulate additional deformation by tracking the pattern of axial surface migration in model folds we predict the distribution of relative deformation intensity in simple step parallel fault bend and fault propagation anticlines in both cases the deformation is partitioned into unique domains we call deformation panels for a given rheology of the folded multilayer deformation intensity will be homogeneously distributed in each deformation panel fold limbs are always deformed the flat crests of fault propagation anticlines are always undeformed two asymmetric deformation panels develop in fault propagation folds above ramp angles exceeding 29 for lower ramp angles an additional more intensely deformed panel develops at the transition between the crest and the forelimb deformation in the flat crests of fault bend anticlines occurs when fault displacement exceeds the length of the footwall ramp but is never found immediately hinterland of the crest to forelimb transition in environments dominated by brittle deformation our models may serve as a first order approximation of the distribution of fractures in fault related folds

a re evaluation of the stratigraphy and evolution of the kohistan arc sequence pakistan himalaya implications for magmatic and tectonic arc building processes new field mapping and structural data combined with published geochemical data from the kohistan arc in the nw himalaya enable a re evaluation of the arc stratigraphy key lithological units and their relationships are more clearly defined permitting the construction of a revised magmatic tectonic history for the arc the oldest units are transitional oceanic type basalts which form the basement to the subduction related sequence arc type gabbroic sheets and plutons intrude the oceanic basalts together these form the kamila amphibolite belt metasediments and basaltic lavas were deposited within an extensional basin onto the kamila amphibolite belt basement this sequence exposed across the arc forms a distinct stratigraphic unit which is formally defined here as the jaglot group sediment charged turbidity currents transported material into the basin whilst submarine eruptions contributed the basaltic component this period of extension culminated in the eruption of high mg boninites of the chalt volcanic group which overlie the rocks of the jaglot group the earliest granitoids of the kohistan batholith predate suturing and intrude the jaglot and chalt sequences at c 100 ma kohistan sutured to asia suturing being accompanied by thickening of the arc with the development of major intra arc shear zones and a penetrative regionally developed steep cleavage at c 85 ma intra arc rifting permitted the emplacement into the arc of the voluminous gabbronorites of the chilas complex which clearly intrudes the kamila amphibolite belt to the south and the jaglot group to the north the chilas complex has been regarded as part of the pre suturing juvenile arc sequence field evidence summarized here show this to be not so heat advection associated with emplacement of the complex caused amphibolite facies regional metamorphism melting of the lower arc and plutonism some of the resultant granitoid plutons were unroofed and eroded during a compressional phase at between 80 and 55 ma before emplacement of further plutons and extrusion of basaltic through to rhyolitic volcanic rocks at between 55 and 40 ma at least three phases of extension and rifting each separated by short lived phases of compression charac terized arc evolution much of the magmatism is controlled by extensional tectonics within the overriding plate of the kind commonly associated with a retreating subduction zone

sedimentology and tectonic implications of the lamayuru complex deep water facies of the indian passive margin indus suture zone ladakh himalaya

role of the tectonic facies concept in orogenic analysis and its application to tethys in the eastern mediterranean region abstract the purpose of this paper is to advocate the use of a tectonic facies concept which aids systematic and objective analysis of orogenic belts the tectonic facies concept as discussed here focuses on the recognition of discrete tectonic settings mainly those exposed at high crustal levels in orogenic belts application of the tectonic facies concept can help field geologists to relate plate scale processes to outcrop geology tectonic facies are recognised based on knowledge of the modern oceans and margins and well constrained land settings tectonic facies analogous to sedimentary facies can be identified from integrated sets of field data and related laboratory studies a number of tectonic facies models can be recognised in this way their identification aids interpretation and comparisons of orogenic belts palinspastic reconstructions require additional information particularly age kinematic and palaeomagnetic data in this paper the tectonic facies concept is tested by application to a well documented mainly high level orogenic segment tethys in the eastern mediterranean area and is found to be an effective way both of the describing and interpreting this region other methods of tectonic analysis e g recognition of tectono stratigraphic terranes may also be found useful in certain settings and can be used in conjunction with the tectonic facies concept

the dras arc two successive volcanic events on eroded oceanic crust abstract the dras arc is recognized as a volcanic arc system in the western part of the indus suture zone and it constitutes the link between the ladakh batholith and the kohistan arc this study is based on detailed mapping of the area between dras kargil and sanku which revealed the following 1 1 the ultramafics of dras and thasgam can be followed across the suru dras ridge and are not intrusive into the arc volcanics but instead constitute the most probably oceanic substratum of these volcanics 2 2 successive volcanic events are distinguished 2 1 a dras i is a variable volcaniclastic series rich in slates and carbonates which can probably be assigned to the albo cenomanian as dated by orbitolines this series is intruded by gabbro diorite and granite and is deformed essentially in the northern part it is unconformably overlain by 2 2 b the dras ii pyroclastics which grade southward into volcanic breccia and thus enable the location of the centres of volcanic activity during this younger period

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

a tectonic model reconciling evidence for the collisions between india eurasia and intra oceanic arcs of the central eastern tethys abstract despite several decades of investigations inferences on the timing and nature of collisions along the mesozoic cenozoic eurasian margin remain controversial we assimilate geological and geophysical evidence into a plate tectonic model for the india eurasia collision that includes continuously closing topological plate polygons constructed from a time dependent network of evolving plate boundaries with synthetic plates constructed for now subducted ocean floor including back arc basins that formed on the southern eurasian margin our model is regionally constrained and self consistent incorporating geophysical data from abyssal plains offshore west australia and east antarctica including jurassic age data from offshore northwest australia limiting much of northern greater india to a 1000 km long indenter originally reaching to the wallaby zenith fracture zone southern eurasia and southeast asia are riddled with dismembered oceanic arcs indicating long lived tethyan intra oceanic subduction this intra oceanic subduction system was well established from cretaceous time in the india eurasia convergence zone in the neotethys which was consumed during greater india s northward trajectory towards eurasia from the early cretaceous fragments of obducted oceanic crust within the yarlung tsangpo suture zone between india and eurasia predominantly date to the late jurassic or mid cretaceous barremian aptian the various ophiolites along strike and a hiatus in subduction related magmatism during the tithonian aptian suggest that there was at least one generation of intra oceanic arc formation whose plate boundary configuration remains uncertain paleomagnetic and magmatic studies suggest that the intra oceanic arc was at equatorial latitudes during the early cretaceous before subduction resumed further north beneath the eurasian margin lhasa terrane with another hiatus in subduction related magmatism along southern lhasa during 80 65 ma possibly as the back arc spreading centre approached the active andean style margin in our model greater india collided with the tethyan intra oceanic arc in paleocene eocene time finally closing the tethyan seaway from mid late eocene time which is consistent with the age of the youngest marine deposits found between india and eurasia geological evidence from the collision zone indicates an age of initial arc continent collision by 52 ma followed by the soft initial continent continent collision between india and eurasia by 44 2 ma this timing is supported by marine geophysical data where the spreading centres in the indian ocean record a drastic decline in seafloor spreading rates and changes in spreading directions first at 52 ma followed by another reorganisation at 43 ma the abandonment of spreading in the wharton basin and the onset of extrusion tectonics in asia by 36 ma are likely indicators of hard complete continent collision and highlight the multi stage collisional history of this margin our continuously evolving network of mid ocean ridge and subduction zone geometries and divergence convergence vectors through time provide a basis for future refinements to assimilate new data and or test alternative tectonic scenarios

mesozoic deep water slope rise sedimentation and volcanism along the north indian passive margin evidence from the karamba complex indus suture zone western ladakh himalaya abstract mesozoic deep water sedimentary and basic volcanogenic rocks defined as the karamba complex are exposed within the indus suture zone of western ladakh n india the karamba complex originated as part of the north indian passive margin in its entirety and does not include exotic melange or accreted oceanic units as recently suggested the complex preserves younger more distal equivalents relative to more proximal deep water slope lamayuru complex and shelf zanskar successions of the north indian passive margin the karamba complex is mainly inverted youngs to the nnw and includes many outcrop scale folds that face nnw the complex was initially emplaced onto the zanskar shelf as three main thrust slices probably in the latest cretaceous and later inverted faulted and sheared during mid late tertiary nw backthrusting that accompanied uplift of the high himalaya sedimentation in the karamba complex began in the mid late triassic with mainly siliciclastic turbidites derived from the indian basement together with redeposited limestones and minor basic volcanics mixed radiolarian sediments siliciclastic turbidites and redeposited shelf derived calciturbidites accumulated in early mid jurassic accompanied by eruption of alkaline volcanic rocks mainly in the mid jurassic the probable cause of the jurassic volcanism was a pulse of crustal extension along the continent ocean transition zone triggered by late stage rifting of india from gondwana as a precursor to its northward drift quartzose sandstone turbidites accumulated on the upper slope in the early cretaceous whereas sedimentation on the lower slope rise was pelagic marked by depositional hiatuses and sediment redeposition during the late cretaceous a switch to mainly calcareous pelagic deposition took place interspersed with radiolarian accumulation on the lower slope rise initial thrust emplacement onto the zanskar shelf in the latest cretaceous is suggested by the absence of post upper cretaceous sediments within the karamba complex

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

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

shyok suture zone n pakistan late mesozoic tertiary evolution of a critical suture separating the oceanic ladakh arc from the asian continental margin abstract the shyok suture zone northern suture of north pakistan is an important cretaceous tertiary suture separating the asian continent karakoram from the cretaceous kohistan ladakh oceanic arc to the south in previously published interpretations the shyok suture zone marks either the site of subduction of a wide tethyan ocean or represents an early cretaceous intra continental marginal basin along the southern margin of asia to shed light on alternative hypotheses a sedimentological structural and igneous geochemical study was made of a well exposed traverse in north pakistan in the skardu area baltistan to the south of the shyok suture zone in this area is the ladakh arc and its late cretaceous mainly volcanogenic sedimentary cover burje la formation the shyok suture zone extends northwards ca 30 km to the late tertiary main karakoram thrust that transported asian mainly high grade metamorphic rocks southwards over the suture zone the shyok suture zone is dominated by four contrasting units separated by thrusts as follows 1 the lowermost askore amphibolite is mainly amphibolite facies meta basites and turbiditic meta sediments interpreted as early marginal basin rift products or trapped tethyan oceanic crust metamorphosed during later arc rifting 2 the overlying pakora formation is a very thick ca 7 km in outcrop succession of greenschist facies volcaniclastic sandstones redeposited limestones and subordinate basaltic andesitic extrusives and flow breccias of at least partly early cretaceous age the pakora formation lacks terrigenous continental detritus and is interpreted as a proximal base of slope apron related to rifting of the oceanic ladakh arc 3 the tectonic melange reconnaissance further east north of the shyok river indicates the presence of redeposited volcaniclastic sediments and thick acid tuffs derived from nearby volcanic centres presumed to lie within the ladakh arc in addition comparison with lower cretaceous clastic sediments maium unit within the northern suture zone west of the nanga parbat syntaxis hunza river reveals notable differences including the presence of terrigenous quartz rich conglomerates serpentinite debris flow deposits and a contrasting structural history the shyok suture zone in the skardu area is interpreted to preserve the remnants of a rifted oceanic back arc basin and components of the asian continental margin in the west hunza river a mixed volcanogenic and terrigenous succession maium unit is interpreted to record syn deformational infilling of a remnant back arc basin foreland basin prior to suturing of the kohistan arc with asia 75 90 ma

the dras arc complex lithofacies and reconstruction of a late cretaceous oceanic volcanic arc in the indus suture zone ladakh himalaya abstract the purpose of this paper is to give an integrated description and interpretation of mainly volcaniclastic sediments related to excellently exposed oceanic volcanic arc successions in the ladakh himalayas the mainly late cretaceous aptian paleocene dras arc complex in the indus suture zone n india is reconstructed as an oceanic arc passing southwards into a proximal to distal forearc apron the arc complex comprises three structural units from west to east these are the suru unit the naktul unit and the nindam formation the suru unit and the naktul unit are unconformably underlain by dissected late jurassic oceanic crust and mantle the suru unit preserves the interior of the arc and is divided into dras 1 and dras 2 sub units the dras 1 sub unit of mid late cretaceous age was intruded by arc plutonics deformed then unconformably overlain by the poorly dated dras 2 sub unit lower tertiary the dras 1 sub unit comprises arc extrusives volcaniclastic and tuffaceous sedimentary rocks and mainly redeposited shallow water limestones the dras 2 sub unit is dominated by coarse volcaniclastics and lava flows passing up into rhythmically layered acidic extrusives with interbedded turbiditic siltstones and siliceous pelagic limestones further east the naktul unit is mainly clastic with large volumes of massive volcaniclastic talus thick bedded debris flows volcaniclastic turbidites and reworked shallow water carbonates pillowed extrusives and ribbon radiolarites are present mainly low in the succession in some areas while pelagic carbonates are abundant near the top the naktul unit is interpreted as a proximal forearc apron the nindam formation in the east is dominated by deep water volcaniclastic turbidites tuffaceous sediments and pelagic carbonates with subordinate debris flows and is interpreted as a distal deep water forearc succession cyclical alternations of mainly volcaniclastics and pelagic carbonates in the nindam formation are thought to reflect relative sea level changes of tectono magmatic and or global eustatic origin the oceanic dras arc complex formed within neotethys in the mid late cretaceous above an assumed northward dipping subduction zone around 79 ma campanian the oceanic arc underwent collisional deformation possibly related to accretion to the trans himalaya ladakh block and or the southern margin of eurasia to form an andean type active continental margin the suru unit in the west dras 1 sub unit was deformed then overlain by the mainly acidic dras 2 sub unit however there is no direct evidence that the nindam formation in the east was deformed until the early eocene when final collision of india and eurasia took place with southward thrusting of the dras arc complex this was followed by partial erosion during deposition of the indus molasse and then back thrusting and folding related to uplift of the high himalayas in the later tertiary

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

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

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

40ar 39ar dating of volcanic rocks of the shyok suture zone in north west trans himalaya implications for the post collision evolution of the shyok suture zone abstract 40 ar 39 ar geochronological studies carried out on the khardung volcanics of ladakh india and our earlier ar ar results from the volcanics of the shyok suture along with the available geological and geochemical data provide good constraints for post collision evolution of the shyok suture zone whole rock samples from the shyok volcanics yielded disturbed age spectra and we have demonstrated earlier that the youngest tectonic event in the shyok suture zone responsible for the thermal disturbance of these samples is karakoram fault activation at 14 ma contrastingly whole rock samples from the khardung volcanics which are in tectonic contact with these shyok volcanics and are exposed in the form of thick rhyolitic and ignimbritic flows yielded undisturbed age spectra and good plateau ages the whole rock plateau ages of two rhyolite samples are 52 8 0 9 and 56 4 0 4 ma we interpret these ages to be the time and duration of emplacement of these volcanics over thickened margin of the continental crust which appears to be coeval with the initiation of the collision between the indian and asian plate the lesser extent of post emplacement isotopic re equilibration in these samples unlike the shyok volcanics indicate that these samples were present in different tectonic settings away from the karakoram fault at the time of deformation in the shyok suture zone we propose that the two volcanic belts of contrasting nature were brought together in juxtaposition by the karakoram strike slip faulting at 14 ma

relicts of an intra oceanic arc in the sapi shergol melange zone ladakh nw himalaya india implications for the closure of the neo tethys ocean in the ladakh zanskar area relicts of both ophiolites and paleo accretionary prism have been preserved in the sapi shergol me lange zone the paleo accretionary prism related to the northward subduction of the northern neo tethys beneath the ladakh asian margin mainly consists of tectonic intercalations of sedimentary and blueschist facies rocks whole rock chemical composition data provide new constraints on the origin of both the ophiolitic and the blueschist facies rocks the ophiolitic rocks are interpreted as relicts of the south ladakh intra oceanic arc that were incorporated in the accretionary prism during imbrication of the arc the blueschist facies rocks were previously interpreted as oceanic island basalts oib but our new data suggest that the protolith of some of the blueschists is a calc alkaline igneous rock that formed in an arc environment these blueschists most likely originated from the south ladakh intra oceanic arc this arc was accreted to the southern margin of asia during the late cretaceous and the buried portion was metamorphosed under blueschist facies conditions following oceanic subduction the external part of the arc was obducted to form the south ladakh ophiolites or was incorporated into the sapi shergol me lange zone the incorporation of the south ladakh arc into the accretionary prism implies that the complete closure of the neo tethys likely occurred by eocene time

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

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

geochemistry of dras volcanics and the evolution of the indus suture ophiolites abstract the indus suture zone with many ophiolite occurrences represents the northern limit of the tethyan himalaya the volcanic rocks of the dras ophiolite zone exhibit low tio2 k2o p2o5 sio2 pb rb ba sr and zr concentrations and lower la yb ratios than the intraplate tholeiites intercalation of marine sediments presence of pillow lavas low k2o low to moderate tio2 high mgo cao tio 2 and al 2 o 3 tio 2 flat ree patterns with lower la n sm n ratios and increase of sio2 feo t and tio2 with the fractionation indicate that they are island arc tholeiites similar to lavas of late cretaceous age in cyprus and oman these volcanics are postulated to have been derived from a tholeiitic magma generated by a high degree of partial melting and fractionation of mafic phases prior to the crystallization of plagioclase the island arc tholeiitic volcanism the lack of major ca volcanic activity and the reported blueschist metamorphism of the indus ophiolites suggest a palaeo island arc development along the indus suture zone along which the tethys oceanic crust was consumed

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

sedimentary processes in modern and ancient oceanic arc settings evidence from the jurassic talkeetna formation of alaska and the mariana and tonga arcs western pacific abstract sediment deposited around oceanic volcanic ares potentially provides the most complete record of the tectonic and geochemical evolution of active margins the use of such tectonic and geochemical records requires an accurate understanding of sedimentary dynamics in an arc setting processes of deposition and reworking that affect the degree to which sediments represent the contemporaneous volcanism at the time of their deposition we review evidence from the modern mariana and tonga arcs and the ancient arc crustal section in the lower jurassic talkeetna formation of south central alaska and introduce new data from the mariana arc to produce a conceptual model of volcaniclastic sedimentation processes in oceanic arc settings all three arcs are interpreted to have formed in tectonically erosive margin settings resulting in long term extension and subsidence debris aprons composed of turbidites and debris flow deposits occur in the immediate vicinity of arc volcanoes forming relatively continuous mass wasted volcaniclastic records in abundant accommodation space there is little erosion or reworking of old volcanic materials near the arc volcanic front tectonically generated topography in the forearc effectively blocks sediment flow from the volcanic front to the trench although some canyons deliver sediment to the trench slope most volcaniclastic sedimentation is limited to the area immediately around volcanic centers arc sedimentary sections in erosive plate margins can provide comprehensive records of volcanism and tectonism spanning 10 my the chemical evolution of a limited section of an oceanic arc may be best reconstructed from sediments of the debris aprons for intervals up to 20 my but no longer because subduction erosion causes migration of the forearc basin crust and its sedimentary cover toward the trench where there is little volcaniclastic sedimentation and where older sediments are dissected and reworked along the trench slope

sedimentary and geochemical evolution of the dras forearc basin indus suture ladakh himalaya india the nindam formation of the indus suture zone represents the forearc basin to the dras kohistan volcanic arc which was generated in an intraoceanic setting during mid cretaceous time and accreted to the margin of eurasia during late cretaceous time the nindam formation comprises volcaniclastic sediment and pelagic carbonate deposited in cyclic influxes of high density sheet like turbidites with locally well defined channel morphologies debris flow deposits as much as 5 m thick that rework older material are volumetrically 5 of the sequence a fine grained basal section is succeeded by several hundred meters of cyclic sandy turbidites and finally a more shaley top this large scale variation may be linked to tectonic controls on arc activity while individual sandy packages 50 100 m thick are inferred to have a glacioeustatic origin sedimentation mirrors similar patterns observed in the modern mariana and tonga forearcs the lack of major unconformities and large scale reworking suggests that the volcaniclastic sedimentary rocks should form a relatively complete record of geochemical change in the arc source the sediment trace and rare earth element ree signature is similar to that of the dras and chalt volcanic rocks erupted at the volcanic front during the intraoceanic phase of activity and is distinct from the kardung volcanic group erupted during the continental arc phase following collision with the eurasian margin nd isotopes also support an intraoceanic origin the sedimentary rocks show either no or slight light ree enrichment similar to modern sediments from the mariana arc as well as the volcanic and intrusive core of the dras kohistan arc the overall chemistry of the dras kohistan arc is thus more depleted in light ree than continental crust our data do not support models that propose continental crust being formed along intraoceanic active margins

geochemical and isotopic constraints on the age and origin of the nidar ophiolitic complex ladakh india implications for the neo tethyan subduction along the indus suture zone abstract the nidar ophiolite complex is exposed within the indus suture zone in eastern ladakh india the suture zone is considered to represent remnant neo tethyan ocean that closed via subduction as the indian plate moved northward with respect to the asian plate the two plates ultimately collided during the middle eocene the nidar ophiolite complex comprises a sequence of ultra mafic rocks at the base gabbroic rocks in the middle and volcano sedimentary assemblage on the top earlier studies considered the nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage however present study based on new mineral and whole rock geochemical and isotopic data on bulk rocks and mineral separates indicate their generation and emplacement in an intra oceanic subduction environment the plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element ree patterns the gabbroic rocks in particular show strong positive sr and eu anomalies in their ree and spidergram patterns probably indicating plagioclase accumulation depletion in high field strength elements hfse in the spidergram patterns may be related to stabilization of phases retaining the hfse in the subducting slab and or fractional crystallization of titano magnetite phases the high radiogenic nd and low radiogenic sr isotopic ratios for these rocks exclude any influence of continental material in their genesis implying an intra oceanic environment nine point mineral whole rock sm nd isochron corresponds to an age of 140 32 ma with an initial 143nd 144nd of 0 513835 0 000053 end t 7 4 this age is consistent with the precise early cretaceous age of hauterivian 132 2 to 127 1 6 ma to aptian 121 1 4 to 112 1 1 ma for the overlying volcano sedimentary radiolarian bearing chert sequences based on well preserved radiolarian fossils kojima s ahmad t tanaka t bagati t n mishra m kumar r islam r khanna p p 2001 early cretaceous radiolarians from the indus suture zone ladakh northern india in news of osaka micropaleontologists nom spec vol 12 257 270 and cooling ages of 110 130 ma based on 39ar 40ar for nidar spontang ophiolitic rocks maheo g berttrand h guillot s villa i m keller f capiez p 2004 the south ladakh ophiolites nw himalaya india an intra oceanic tholeiitic arc origin with implications for the closure of the neo tethys chem geol 203 273 303 as these gabbroic and volcanic rocks are interpreted to be arc related the new sm nd age data may indicate that intra ocean subduction in the neo tethyan ocean may have started much before 140 32 ma as this date is interpreted as the age of crystallization of the arc magma present and published age data on the arc magmatic rocks from the indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic during 140 32 ma when the arc was immature through intermediate andesitic granodioritic at 100 ma to more felsic rhyolitic dioritic magmatism at 50 45 ma when the indian and the asian plates collided

differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes abstract records of ancient intraoceanic arc activity now preserved in continental suture zones are commonly used to reconstruct paleogeography and plate motion and to understand how continental crust is formed recycled and maintained through time however interpreting tectonic and sedimentary records from ancient terranes after arc continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others in this synthesis we examine what is lost and what is preserved in the translation from modern processes to the ancient record of intraoceanic arcs composition of accreted arc terranes differs as a function of arc continent collision geometry forward facing collision can accrete an oceanic arc on to either a passive or an active continental margin with the arc facing the continent and colliding trench and forearc side first in a backward facing collision involving two subduction zones with similar polarity the arc collides backarc first with an active continental margin the preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision rather than tectonic erosion the prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent arc systems are most likely to undergo tectonic accretion shortly before forward facing collision with a continent and thus most forearc and accretionary prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity when sediment flux to the trench was greatest and tectonic accretion prevailed collision geometry and tectonic erosion vs accretion are important controls on the ultimate survival of material from the trench forearc arc massif intra arc basins and backarc basins and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts oblique plate convergence and arc rifting forward facing collision involves substantial recycling melting and fractionation of continent derived material during and after collision and so produces melts rich in silica and incompatible trace elements as a result forward facing collision can drive the composition of accreted arc crust toward that of average continental crust

formation of melanges in the indus suture zone ladakh himalaya by successive subduction related collisional and post collisional processes during late mesozoic late tertiary time

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

was late cretaceous paleocene obduction of ophiolite complexes the primary cause of crustal thickening and regional metamorphism in the pakistan himalaya

zircon u pb and hf isotopic constraints on petrogenesis of the cretaceous tertiary granites in eastern karakoram and ladakh india abstract multiple subduction events occurred preceding the collision of greater india with the karakoram terrane that consumed the neotethyan ocean between early cretaceous and eocene time zircon u pb dating and hf isotope analyses of granitic rocks collected from the karakoram terrane and ladakh batholith have been conducted to constrain these geological processes undeformed ladakh batholith granodiorite yielded zircon u pb ages of 68 and 64 ma with ehf t values of 6 4 and 10 3 and three diorites near leh and darbuk gave zircon u pb ages of 50 4 51 0 ma and ehf t values of 7 4 to 8 9 indicating that the paleocene eocene was the most important period of granitic magmatism that derived from a juvenile source three tonalite granodiorite enclaves at skyangpoche within the karakoram batholith have zircon u pb ages of 101 103 ma with ehf t values of 2 3 to 3 7 indicating generation of granitic rocks by partial melting of the karakoram basement three samples of the miocene karakoram batholith from around darbuk yielded ages of 16 6 19 1 ma with ehf t values of 8 5 and 10 5 that indicate an input of ancient crust from the indian plate granodiorite within the karakoram metasedimentary sequence zircon u pb age 74 ma ehf t of 5 4 from the tangtse gorge and granite around muglib zircon u pb age of 63 and 56 ma ehf t of 6 8 and 6 0 indicate similar geochronological and isotopic characteristics to those of the ladakh batholith thus the time resolved hf isotopic compositions of magmatic zircons from the granites in the karakoram and ladakh batholith show a large variation that indicate their derivation from both ancient and juvenile continental crusts in active continental margin since at least the mid cretaceous

early jurassic volcanic rocks in the xiongcun district southern lhasa subterrane tibet implications for the tectono magmatic events associated with the early evolution of the neo tethys ocean abstract early mesozoic late triassic to middle jurassic igneous rocks in the southern lhasa subterrane tibet record important information on the early tectono magmatic evolution of the neo tethys ocean this paper presents petrological geochronological and geochemical data for the xiongcun formation ignimbrites to constrain the petrogenesis and tectonic setting of these rocks in the southern lhasa subterrane the xiongcun formation is dominated by andesitic and dacitic rocks these rocks yield early jurassic 195 176 ma zircon u pb ages and display typical arc like geochemical signatures being enriched in large ion lithophile elements e g rb ba and u and depleted in high field strength elements e g nb ta and ti sr nd pb hf isotopic compositions are highly depleted these chemical and isotopic data suggest that the xiongcun formation ignimbrites probably formed in an intra oceanic island arc setting related to the northward subduction of the neo tethys oceanic slab the parental magmas were derived from a depleted mantle source modified by fluids released from the neo tethys oceanic slab combined with previously reported data we suggest that the volcanic rocks in the early jurassic xiongcun and yeba formations of the southern lhasa subterrane were generated by a single subduction system but developed on oceanic and continental crust respectively

reconstructing early himalayan tectonic evolution and paleogeography from tertiary foreland basin sedimentary rocks northern india the latest paleocene middle eocene subathu formation and the oligocene miocene dagshai and kasauli formations of the indian foreland basin record the early evolution of the himalayan fold thrust belt sandstone petrography of the subathu formation shows a predominantly recycled sedimentary source with a distinct ophiolitic and volcanic influence that was drastically reduced by the time of deposition of the dagshai formation sandstones in the dagshai and kasauli formations consist predominantly of metapelitic detritus the metamorphic grade of metapelitic lithic grains increases with time from dominantly very low grade at the base of the dagshai formation to dominantly low grade in the kasauli sandstones mudstone geochemistry documents the presence of a mafic ultramafic source during the time of deposition of the subathu formation that becomes significantly less important by the time of deposition of the dagshai formation compositions of subathu formation detrital spinels show they were either derived from both mid ocean ridge basalt type and arc type ophiolites or from an ophiolite of composite origin and that southerly derivation from the deccan trap continental flood basalts is unlikely kasauli formation garnet compositions suggest derivation from medium grade metamorphic rocks to amphibolite facies subathu formation composition reflects provenance influence from the indus suture zone during latest paleocene middle eocene time indicating initiation of continent continent collision and development of the foreland basin by this time suture zone influence was drastically reduced by the time of deposition of the dagshai formation when the embryonic thrust belt provided a barrier sufficient to partially separate the suture zone from the himalayan foreland basin the first appearance of himalayan metamorphic detritus occurs in the dagshai formation at the close of oligocene time whereas the kasauli formation records erosion to deeper metamorphic levels during earliest miocene time the occurrence of garnet and higher grade metamorphic lithic grains during early neogene time is coincident with the timing of displacement along the main central thrust and south tibetan detachment zone composition of early foreland basin sediments from pakistan balakot murree and kamlial formations to nepal bhainskati and dumri formations and bangladesh kopili barail formations surma group indicates diachronous arrival of ophiolitic to low grade metamorphic detritus derived respectively from the indus suture and early himalayan thrust sheets in the north this is consistent with progressively later closure of neotethys along the suture from latest paleocene time in the west to eocene time or even later in the east

saturn s zonal wind profile in 2004 2009 from cassini iss images and its long term variability abstract five years of cassini imaging science subsystem images from 2004 to 2009 are analyzed in this work to retrieve global zonal wind profiles of saturn s northern and southern hemispheres in the methane absorbing bands at 890 and 727 nm and in their respective adjacent continuum wavelengths of 939 and 752 nm a complete view of saturn s global circulation including the equator at two pressure levels in the tropopause 60 mbar to 250 mbar with the mt filters and in the upper troposphere from 350 mbar to 500 mbar with the cb filter set is presented both zonal wind profiles available at the supplementary material section show the same structure but with significant differences in the peak of the eastward jets and the equatorial region including a region of positive vertical shear symmetrically located around the equator between the 10 c

the tectonic evolution of the kohistan karakoram collision belt along the karakoram highway transect north pakistan the kohistan arc terrane comprises an intra oceanic island arc of cretaceous age separating the indian plate to the south from the karakoram asian plate to the north within the indus suture zone of north pakistan the intra oceanic arc volcanics chalt dras group were built on a foundation of dominantly mid ocean ridge basalt morb related amphibolites of the kamila group the subarc magma chamber is represented by multiple intrusions of a huge gabbro norite complex chilas complex which includes some ultramafic assemblages of residual mantle harzburgite and dunite layered cumulates and hornblendites cut by late stage dikes of hornblende plagioclase pegmatites the chilas complex norites intrude the gilgit metasediments of lower amphibolite and greenschist facies in northern kohistan which also form xenolithic roof pendants within the top of the chilas complex along the southern margin of kohistan jijal and sapat complex ultramafics dunites harzburgites and websterites form remnant suprasubduction zone ophiolitic mantle rocks along the hanging wall of the main mantle thrust the cretaceous obduction plane along which kohistan was emplaced onto indian plate rocks garnet granulites of the jijal complex formed at 12 14 kbars represent original magmatic lower crustal rocks subducted to depths of at least 45 km and metamorphosed during high pressure and high temperature subduction of earlier arc related rocks obduction of the sapat ophiolite and kohistan arc occurred between 75 and 55 ma the closure of the shyok suture zone separating kohistan from the karakoram plate must have occurred prior to 75 ma the age of the jutal basic dikes which crosscut the closure related fabrics mainly late north directed backthrusting in the lower hunza valley andean type granitoid gabbrodiorite granodiorite granite emplacement along the kohistan ladakh batholith ended at the time of india asia collision 60 50 myr ago postcollisional crustal thickening along the karakoram led to multiple episodes of metamorphism from latest cretaceous and throughout the tertiary sillimanite grade metamorphism in hunza was actually pre india asia collision and may have resulted from the earlier kohistan collision localized and sporadic crustal melting episodes across northern kohistan indus confluence and parri granite sheets and the southern karakoram hunza dikes and sumayar and mango gusar leucogranites occurred from 51 to 9 ma and culminated in the huge baltoro monzogranite leucogranite intrusion 25 21 myr ago a vast network of leucogranitic and pegmatitite dikes containing gem quality aquamarine muscovite tourmaline garnet biotite quartz are younger than 5 ma and form the final phase of intrusion in the haramosh area and parts of the southern karakoram area

the spongtang massif in ladakh nw himalaya an early cretaceous record of spontaneous intra oceanic subduction initiation in the neotethys abstract the spongtang massif is a remnant of neotethyan ocean crust emplaced onto the indian passive margin along the indus yarlung tsangpo suture in the nw himalayan region of ladakh the age tectonic evolution and timing of ophiolite obduction are critical to our understanding of the mechanisms via which entire oceans are formed consumed and partly preserved before the onset of terminal continent continent collisions geochemistry of the gabbro and basaltic units suggest the presence of both morb type and primitive arc related mafic rocks zircons extracted from the spongtang massif gabbros yield u pb shrimp ages of 136 133 ma with initial ehf values of 14 to 16 indicating early cretaceous juvenile depleted mantle sources devoid of contamination by older continental crust previously middle jurassic 177 ma zircon ages were obtained from gabbro and we suggest these represent morb type neotethyan oceanic crust through which a younger intra oceanic island arc spong arc developed in response to subduction initiation during the early cretaceous 136 ma our zircon ages are consistent with early cretaceous ages obtained for radiolarian cherts within the spong arc complex subduction beneath the spong arc continued until its collision with the northern indian continental margin during the early eocene we suggest that the spongtang massif is equivalent to the nearby dras island arc terrane intra oceanic subduction beneath this system was possibly initiated along nne ssw trending transform faults in the neotethyan ocean along which different ages of ocean crust was juxtaposed thereby development of the early cretaceous spong arc is superimposed on the older jurassic spongtang n morb crust the juvenile hf signature indicates the subduction system that spawned the spong island arc was not related to the coeval trans himalayan ladakh gangdese arc that developed along the southern margin of eurasia the age composition and nature of geological relationships with the underlying indian rocks indicate the spong arc was a juvenile intra oceanic terrane that first collided with india before the onset of final continent continent collision therefore final late eocene neotethys closure was between the kohistan ladakh eurasian continental arc and the already inactive indian spongtang margin

geochemistry and petrogenesis of ultramafic and mafic plutonic rocks of the dras ophiolitic melange indus suture northwest himalaya geochemical data are presented for a suite of ultramafic and related rocks from the dras ophiolitic melange of the indus suture zone in the western himalaya harzburgites from the suite have highly refractory chemistry lherzolites from the suite represent modified mantle material and are comparable to potential source rocks for morb and to the lherzolites of the bay of islands ophiolites cumulus dunite pyroxenite and gabbro units contain olivine chromite clinopyroxene and plagioclase as the major cumulus phases orthopyroxene is absent as a cumulus phase and in this respect the dras ophiolite differs from the marum betts cove and troodos ophiolites however the dras cumulates are similar to the vourinos and bay of islands cumulate sequence and are consistent with accumulation of low pressure liquidus phases of mid oceanic ridge type magmas magmas parental to the dras cumulate rocks contained high 100 mg mg fe2 ratios of 77 79 high ni cr and possibly ca low ti and depleted lree parent magmas were probably similar to those of normal morb formed by two stage or dynamic melting processes in the mantle peridotite fabrics suggest high temperature plastic mantle deformation disruption serpentinisation and melange formation were probably produced during emplacement in the indus suture zone

detrital chrome spinel evidence for a neotethyan intra oceanic island arc collision with india in the paleocene abstract models that support a single collision scenario for india and eurasia are incompatible with the evidence that an intra oceanic island arc ioia existed within the neotethyan ocean understanding the spatial and temporal extent of any ioia is crucial for india eurasia collision studies as the entire ocean including any intra oceanic features must have been consumed or emplaced prior to continental collision here we review what is known about the neotethyan ioia and report evidence from sedimentary successions in nw india and southern tibet to constrain when and where it was emplaced we use detrital mineral geochemistry and supporting provenance and age data to identify the source of the sediments and compare the timing of erosion of ioia derived material in both regions detrital chrome spinels extracted from distinct sedimentary horizons in southern tibet sangdanlin and nw india ladakh exhibit similar average geochemical values tio 2 0 09 and 0 24 cr 0 66 and 0 68 and mg 0 45 and 0 53 respectively and supra subduction zone ssz forearc peridotite signatures furthermore they overlap with in situ chrome spinels reported from the spongtang ophiolite in nw india and the sangsang ophiolite in southern tibet as with many of the ophiolitic remnants that crop out in and adjacent to the yarlung tsangpo and indus suture zones ytsz and isz respectively the spongtang and sangsang ophiolites formed in an ioia setting linking the source of the detrital chrome spinels to those analysed from remnant ioia massifs in the ytsz and isz is strong evidence for the emplacement of the ioia onto the indian margin the timing of the ioia collision with india is constrained by the depositional ages of the chrome spinel bearing sediments to the end of the paleocene thanetian in southern tibet and the early eocene in nw india this indirectly provides a maximum age constraint of late paleocene early eocene for intercontinental collision between india and eurasia additionally this study highlights the importance of targeting distinct sedimentary horizons in collision zones to find evidence for discrete tectonic events that may be obfuscated by later collisions

middle cretaceous back arc formation and arc evolution along the asian margin the shyok suture zone in northern ladakh nw himalaya abstract the shyok suture zone of the ladakh palaeovolcanic arc is made of cretaceous volcanosedimentary formations intruded by granodioritic plutons field observations show a tectonic stacking of litho units from different volcanic arc and back arc environments in the western part skardu area the shyok suture zone can be subdivided into two groups 1 the northern group which consists of olistolith basaltic blocks and tuffs the basalts are lree depleted with a lile enrichment and a slight nb depletion suggesting a back arc basin origin 2 the southern group which consists predominantly of andesites that show lree enrichment a flat hree pattern strong nb ta depletion and lile enrichment the volcanic rocks of the southern group appear to have island arc tholeiite iat to calc alkaline affinities in the eastern part of the suture zone nubra shyok area albian to cenomanian age silicoclastic sediments predominate these sediments correspond to a large detrital platform built on the northern part of the ladakh arc at the top these sediments interlayer with basaltic to andesitic lavas these lavas appear to be more differentiated and calc alkaline in nature than the skardu southern group lavas but show similar volcanic arc affinities no evidence of a back arc basin was found in this area our data from these two areas shows a northwest southeast evolution from back arc to arc formations in northern ladakh opening of this back arc basin occurred on the northwestern side of the ladakh arc this back arc was progressively closing eastward the arc itself was more mature in the east resembling the southern tibetan continental arc and was characterised by more continental sedimentation subsequent himalayan tectonometamorphic evolution closure of the back arc basin and deformation along the shyok suture reflects an early asymmetrical geometry along the asian margin and kohistan ladakh arc

shoshonites in southern tibet record late jurassic rifting of a tethyan intraoceanic island arc abstract detailed field mapping combined with a petrologic and geochemical investigation of the zedong terrane within the yarlung tsangpo suture zone provides insights to the evolution of now mostly subducted portions of tethys during the late jurassic the terrane is dominated by volcanic rocks of shoshonitic affinity which were erupted in a submarine oceanic island arc setting the volcanic island arc was built on a basement of oceanic crust and the shoshonites locally overlie a thin section of pillowed island arc tholeiites and red ribbon bedded radiolarian cherts geochemistry of the shoshonites suggests that their development occurred in a setting analogous to that of late miocene to early pliocene fiji and was associated with an arc rifting we speculate that this event may have been a far field response to developments associated with gondwana breakup

field relations and structural constraints for the teru volcanic formation northern kohistan terrane pakistani himalayas abstract the products of late cretaceous paleogene andean style magmatism along the southern margin of asia are preserved in the 2500 km long trans himalayan kohistan ladakh gangdese granitoid batholith together with scattered volcanic outcrops basalts andesites rhyolites and pyroclastics andean type magmatism began in northern pakistan as early as late cretaceous and lasted until terminal collision with india at about 45 ma we present new field and structural data for the teru volcanic formation previously known as the shamran volcanics exposed west of gilgit in the kohistan terrane of the pakistani himalayas the teru volcanic formation comprises a 3 km thick sequence of subaerially erupted mafic to felsic lavas and associated volcaniclastic rocks the kohistan batholith bounds this sequence to the south and the sequence is overthrust to the north by the mid cretaceous chalt volcanic group intra oceanic arc phase along the south verging ghizer thrust these volcanics are lithologically comparable to similar age suites elsewhere in the himalayas this suggests that the paleogeography of southern asia at this time was dominated by an extensive convergent margin province prior to collision with india after india collided with asia the kohistan terrane was uplifted and eroded which removed most of the andean margin phase volcanics

radiolarian evidence for the stratigraphy and palaeo oceanography of the deep water passive margin of the indian plate karamba formation indus suture zone ladakh himalaya abstract new radiolarian biostratigraphical information sheds light on the mesozoic sedimentary tectonic and palaeoceanographic evolution of a south tethyan margin in northern india radiolarian cherts studied here form part of deformed deep water successions within the indus suture zone ladakh himalaya these are defined as the karamba formation and interpreted as the stratigraphically higher and palaeogeographically more distal parts of a passive margin lamayuru group this formation includes radiolarites pelagic carbonates redeposited limestones ferruginous shales sandstones and abundant mafic extrusive rocks radiolarian assemblages of early and late middle jurassic mid cretaceous mid albian to cenomanian and late cretaceous santonian age were obtained from four measured sequences results indicate i long intact jurassic cretaceous successions rather than disrupted melange are present in the karamba formation ii extensive basic volcanism took place during the middle jurassic and can be correlated with an extensional phase affecting the nw indian continental margin iii non calcareous radiolarian rich sediments accumulated during the middle jurassic reflecting the influence either of a broad jurassic equatorial upwelling zone or a more localised coastal upwelling system after drowning of the zanskar clastic shelf in the late albian sedimentation on the distal shelf and upper slope was restricted by bottom current activity late albian cenomanian radiolarites of the karamba formation are contemporaneous with stratigraphie gaps and glauconite phosphorite deposition on the zanskar shelf a well developed eastward boundary current off the northern margin of india may have persisted until near the end of the late cretaceous during the late albian cenomanian current activity and coastal upwelling were probably strong and radiolarian rich sediments accumulated on the distal margin beneath the ccd pelagic limestones accumulated during the turanian over the entire margin possibly related to eustatic sea level rise and consequent reduction in bottom current activity intense oceanic circulation apparently was renewed during the coniacian santonian as indicated by sedimentary hiatuses in the zanskar shelf succession and accumulation of carbonate free radiolarian ooze in the karamba formation

changing source regions of magmas and crustal growth in the trans himalayas evidence from the chalt volcanics and kohistan batholith kohistan northern pakistan the kohistan batholith and chalt volcanics form a major part of the kohistan island arc terrane in northern pakistan they record some 70 80 ma of magmatism within the northwestern himalayan orogen the chalt volcanics are albian aptian mid cretaceous and currently available rbsr age data for the batholith indicate an intrusive age span of 102 to 30 ma the volcanics are composed of medium k calc alkaline andesites and low k high mg tholeiites some of which have boninitic and basaltic komatiitic chemistry three intrusive stages are recognised in the batholith 1 110 90 ma comprises low k trondhjemites and medium high k calc alkaline gabbro diorites with associated hornblendite cumulates 2 85 40 ma comprises low high k calc alkaline gabbro diorites with hornblendite cumulates granodiorites and granites and 3 circa 30 ma comprises biotite muscovite garnet leucogranites 87sr 86sr0 for the batholith range between 0 7039 and 0 7052 four magmatic source regions sce 1 sce 4 have been identified sce 1 is a variably metasomatised mantle wedge situated above an active subduction zone during stages 1 and 2 sce 2 is a harzburgite depleted with respect to major elements and incompatibles whilst retaining subduction related trace element ratios sce 2 melted during stage 1 within a fore arc position during the subduction of young hot oceanic crust to provide the necessary extra thermal input for harzburgite anatexis melts from sce 2 produced the high mg tholeiitic volcanics sce 3 melted during stage 1 to produce the low k trondhjemites and it is envisaged as incompatible element depleted primitive arc crust with a similar composition to the depleted chalt volcanics sce 4 melted at 30 ma during stage 3 as india underthrust eurasia frictional heating and dehydration of the indian plate caused crustal anatexis within the deep kohistan arc and these melts formed the stage 3 leucogranites the low 87sr 86sr initial ratios for the great bulk 95 of the batholith indicate that it represents a major juvenile addition to the continental crust this conclusion has important implications for crustal growth theories of island arc accretion and batholith underplating