polyphase tectonic subsidence evolution of the vienna basin inferred from quantitative subsidence analysis of the northern and central parts the vienna basin is a tectonically complex neogene basin situated at the alpine carpathian transition this study analyzes a detailed quantification of subsidence in the northern and central parts of the vienna basin to understand its tectonic subsidence evolution about 200 wells were used to arrange stratigraphic setting and wells reaching the pre neogene basement were analyzed for subsidence to enhance the understanding of the regional subsidences the wells were sorted into ten groups based on their position on major fault blocks in the early miocene subsidence was slow and along e w to ne sw trending axis indicating the development of thrust controlled piggyback basins during the late early miocene data show abruptly increasing subsidence making the initiation of the vienna pull apart basin system from the middle miocene the tectonic subsidence curves show regionally different patterns the tectonic subsidence during the middle miocene varies laterally across the vienna basin and the differential subsidence can be related to the changing tensional regime of weakening transtension and strengthening extension toward the late middle miocene from the late middle miocene to the late miocene the tectonic subsidence occurred dominantly along the regional active faults and corresponds to the axis of e w trending extension of the western parts of the pannonian basin system in the quaternary the vienna basin has been reactivated and resulted in subsidence along the ne sw trending vienna basin transfer fault system

structure of the north indian continental margin in the ladakh zanskar himalayas implications for the timing of obduction of the spontang ophiolite india asia collision and deformation events in the himalaya the collision of india and asia can be defined as a process that started with the closing of the tethyan ocean that during mesozoic and early tertiary times separated the two continental plates following initial contact of indian and asian continental crust the indian plate continued its northward drift into asia a process which continues to this day in the ladakh zanskar himalaya the youngest marine sediments both in the indus suture zone and along the northern continental margin of india are lowermost eocene nummulitic limestones dated at similar 54 ma along the north indian shelf margin southwest facing folded palaeocene lower eocene shallow marine limestones unconformably overlie highly deformed mesozoic shelf carbonates and allochthonous upper cretaceous shales indicating an initial deformation event during the latest cretaceous early palaeocene corresponding with the timing of obduction of the spontang ophiolite onto the indian margin it is suggested here that all the ophiolites from oman along western pakistan bela muslim bagh zhob and waziristan to the spontang and amlang la ophiolites in the himalaya were obducted during the late cretaceous and earliest palaeocene prior to the closing of tethys

age and structure of the shyok suture in the ladakh region of northwestern india implications for slip on the karakoram fault system a precise age for the collision of the kohistan ladakh block with eurasia along the shyok suture zone ssz is one key to understanding the accretionary history of tibet and the tectonics of eurasia during the india eurasia collision knowing the age of the ssz also allows the suture to be used as a piercing line for calculating total offset along the karakoram fault which effectively represents the se border of the tibetan plateau and has played a major role in plateau evolution we present a combined structural geochemical and geochronologic study of the ssz as it is exposed in the nubra region of india to test two competing hypotheses that the ssz is of late cretaceous or alternatively of eocene age coarse continental strata of the saltoro molasse mapped in this area contain detrital zircon populations suggestive of derivation from eurasia despite the fact that the molasse itself is deposited unconformably onto kohistan ladakh rocks indicating that the molasse is postcollisional the youngest population of detrital zircons in these rocks approximately 92 ma and a u pb zircon date for a dike that cuts basal molasse outcrops approximately 85 ma imply that deposition of the succession began in the late cretaceous this establishes a minimum age for the ssz and rules out the possibility of an eocene collision between kohistan ladakh and eurasia our results support correlation of the ssz with the bangong suture zone in tibet which implies a total offset across the karakoram fault of approximately 130 190 km

provenance of lower cretaceous wolong volcaniclastics in the tibetan tethyan himalaya implications for the final breakup of eastern gondwana abstract lower cretaceous volcanic lithic arenites widely distributed in the tethyan himalaya provide insights into the continental breakup of eastern gondwana in southern tibet they are represented by the wolong volcaniclastics the volcanic rocks that contributed clastic material to the lower parts of this unit were predominantly alkali basalts whereas rhyolitic dacitic volcanism becomes the predominant source of the upper strata geochemical analyses of basaltic grains and of detrital cr spinels from the wolong volcaniclastics demonstrate the alkaline character of the volcanism and suggest within plate tectonic setting for the volcanism zircon u pb ages confirm that this volcanism continued from 140 ma to 119 ma hf isotope data on these early cretaceous zircons indicate that their parental magmas were mantle derived but in the later stage of magmatic activity mantle derived magmas were mixed with partial melts derived from the continental crust the lower cretaceous volcaniclastics occur along a broad belt paralleling the northern margin of greater india the onset of volcaniclastic deposition in the himalayas appears to become progressively younger toward the west but it ended synchronously during the late albian 102 ma the low volume of volcanic rocks and their intra plate tectonic setting suggest that they are the result of decompressional melting along extensional deep seated fractures cross cutting the continental crust and reflect changes in regional intra plate tectonic stresses when greater india began to separate from the australia antarctica supercontinent

compositional trends in arc related deep marine sand and sandstone a reassessment of magmatic arc provenance detrital modes for 524 deep marine sand and sandstone samples recovered on circum pacific caribbean and mediterranean legs of the deep sea drilling project and the ocean drilling program form the basis for an actualistic model for arc related provenance this model refines the dickinson and suczek 1979 and dickinson and others 1983 models and can be used to interpret the provenance tectonic history of ancient arc related sedimentary sequences four provenance groups are defined using qfl qmkp lmlvls and lvflvmilvl ternary plots of site means 1 intraoceanic arc and remnant arc 2 continental arc 3 triple junction and 4 strike slip continental arc intraoceanic and remnant arc sands are poor in quartz mean qfl q 75 they are predominantly composed of plagioclase feldspar and volcanic lithic fragments continental arc sand can be more quartzofeldspathic than the intraoceanic and remnant arc sand mean qfl q values as much as 10 mean qfl f values as much as 65 and mean qmkp qm as much as 20 and has more variable lithic populations with minor metamorphic and sedimentary components the triple junction and strike slip continental groups compositionally overlap both are more quartzofeldspathic than the other groups and show highly variable lithic proportions but the strike slip continental group is more quartzose modal compositions of the triple junction group roughly correlate with the qfl transitional arc field of dickinson and others 1983 whereas the strike slip continental group approximately correlates with their dissected arc field

observations and modelling of first year ice growth and simultaneous second year ice ablation in the prydz bay east antarctica the seasonal cycle of fast ice thickness in prydz bay east antarctica was observed between march and december 2012 in march we observed a 0 16 m thickness gain of 0 22 m thick first year ice fyi while 1 16 m thick second year ice syi nearby simultaneously ablated by 0 59 m a 1 d thermodynamic sea ice model was applied to identify the factors that led to the simultaneous growth of fyi and melt of syi the different evolutions were explained by the difference in the conductive heat flux between the fyi and syi as the fyi was thin there was a large temperature gradient between the ice base and the colder ice surface this generated an upward conductive heat flux which was larger than the heat flux from the ocean to the ice base yielding basal growth of ice in the case of the thicker syi the temperature gradient and hence the conductive heat flux were smaller and not sufficient to balance the oceanic heat flux at the ice base yielding basal ablation penetration of solar radiation affected the conductive heat flux in both cases and the model results were sensitive to the initial ice temperature profile and the uncertainty of the oceanic heat flux

direct stratigraphic dating of india asia collision onset at the selandian middle paleocene 59 1 ma the collision of india with asia had a profound influence on cenozoic topography oceanography climate and faunal turnover however estimates of the time of the initial collision when indian continental crust arrived at the transhimalayan trench remain highly controversial here we use radiolarian and nannofossil biostratigraphy coupled with detrital zircon geochronology to constrain firmly the time when asian derived detritus was first deposited onto india in the classical sangdanlin section of the central himalaya which preserves the best paleocene stratigraphic record of the distal edge of the indian continental rise deep sea turbidites of quartzarenite composition and indian provenance are replaced upsection by turbidites of volcano plutoniclastic composition and asian provenance this sharp transition occurs above abyssal cherts yielding radiolaria of paleogene radiolarian zones rp 4 6 and below abyssal cherts containing radiolaria of zone rp6 and calcareous shales with nannofossils of the paleocene calcareous nannofossil zone cnp 7 constraining the age of collision onset to within the middle paleocene selandian the youngest u pb ages yielded by detrital zircons in the oldest asia derived turbidites indicate a maximum depositional age of 58 1 0 9 ma collision onset is thus mutually constrained by biostratigraphy and detrital zircon chronostratigraphy as 59 1 ma this age is both more accurate and more precise than those previously obtained from the stratigraphic record of the northwestern himalaya and suggests that within the resolution power of current methods the india asia initial collision took place quasi synchronously in the western and central himalaya

the timing of india asia collision onset facts theories controversies abstract the timing of initial collision between india and asia has remained controversial for half a century this paper attempts to review this crucial and hotly debated argument describing first the different methods used to constrain the age of collision and discussing next the rationale results inferences and problems associated with each we conclude that stratigraphy represents the best direct way to unravel collision chronology other methods focusing on the magmatic metamorphic or paleomagnetic record provide additional fundamental constraints but cannot provide a robust direct estimate of collision onset initial collision in the central eastern himalaya is dated directly at the middle paleocene 59 1 ma by the abrupt change in sediment provenance recorded in trench settings the quasi synchronous unconformities documented along both tethyan passive margin of india and active margin of asia from tibet to zanskar ladakh confirm that orogeny was underway at the close of the paleocene 56 ma well before the disappearance of marine seaways in the himalaya during the early middle eocene 50 45 ma sedimentary evolution and provenance changes in marine to fluvio deltaic successions are recorded synchronously within error from the western to the central eastern himalaya failing to provide conclusive evidence for diachronous collision these coherent observations are hard to reconcile with three widely cited hypotheses invoking either paleogene arc continent collision or late cretaceous ophiolite obduction or the protracted existence of a greater india basin which are all not favored after discussing the geological evidence critically point by point a scenario no more complex than the one involving solely the passive continental margin of india and the active continental margin of asia is needed to explain the geological evolution of the nascent himalaya the collision between the tethys himalaya and the transhimalayan arc trench system does represent the collision between india and asia because the yarlung zangbo ophiolite is the forearc basement of the asian active margin its obduction onto india could not have preceded the initial closure of neo tethys ophiolite obduction began when collision began in the middle paleocene

field documentation and genesis of back structures in ductile and brittle regimes from the foreland part of a collisional orogen examples from the darjeeling sikkim lesser himalaya india in the foreland side of an orogen thrust related structures develop that verge towards the foreland fore thrusts although much less abundant structures with opposite vergence i e towards hinterland named back structures also exist we report back structures exposure scale back thrusts and associated folds from the darjeeling sikkim lesser himalaya india these structures occur mainly in three back structure zones bsz a b and c back structures probably originated in the ductile regime and continued in the brittle domain tectonic setting of the study area such as critical taper duplexing etc indicates a good potential for the presence of back structures in this region along with the previous work on back structures in collisional orogens himalaya in particular these structures seem to be ubiquitous the correlation of field observations with tectonics indicate that mechanisms e g critical taper sub surface barriers and passive roof duplex played roles in forming back structures in this part of the sikkim lesser himalaya

arcuate pamir in the paleogene insights from a review of stratigraphy and sedimentology of the basin fills in the foreland of ne chinese pamir western tarim basin abstract the tectonic evolution of the pamir bears essential information for understanding intracontinental tectonic processes within the context of india asia convergence however it is unclear whether the arcuate shape of the pamir is entirely the result of the india asia collision or may have been in part an inherited pre cenozoic feature in this study we address the evolution of the ne chinese pamir during the paleogene by reviewing the stratigraphy of twelve sections in the western tarim basin and the establishment of sedimentary facies the results indicate three episodes of deposition of alluvial coarse sediments in the foreland regions of ne chinese pamir during the 1 early paleocene 2 late paleocene to early eocene and 3 middle eocene to oligocene respectively these are correspondingly attributed to 1 retroarc deformation in an andean type margin of the southern asia during subduction of the neo tethys ocean 2 the immediate response in the pamir to the india asia collision and 3 continued india asia convergence the alluvial conglomerates with grain size up to 5 10 cm imply a transport distance

provenance of the lower tertiary murree redbeds hazara kashmir syntaxis pakistan and initial rising of the himalayas abstract the murree supergroup of northern pakistan is represented by an over 6 km thick succession of deltaic redbeds and intercalated impure foraminiferal limestones of latest palcocene to middle eocene ilerdian to lutetian age cropping out in the northern part of the hazara syntaxis and by redbeds of younger age early middle eocene to early miocene cropping out in the southern part of the syntaxis rawalpindi area the quartzolithic composition of the murree redbeds testifies to a collision orogen provenance detritus was derived from a suture belt including thrust sheets of metasedimentary and subordinately sedimentary rocks volcanic or volcaniclastic rocks and ophiolites phyllite rock fragments are most common in the ilerdian sandstones whereas volcanic and carbonate rock fragments are more abundant in the lutetian sandstones minor quantities of chert and serpentineschist indicating contribution from uplifted subduction complex sources as well as siltstone shale and limestone grains are invariably present detrital modes of sandstones and southwestward progradation of tertiary clastic wedges both testify to provenance from the proto himalayan chain located to the north and uplifted since the very first stages of the india asia continental collision at the end of the paleocene the coeval chulung la redbeds of the tethys himalaya instead consisting of volcanic and subordinate ophiolitic detritus testify to exclusive provenance from the obducting trans himalayan are trench system this major petrographic difference may be accounted for by the different structural setting of the chulung la piggy back and murree foreland basins these two distinct collisional basins have been separated probably since the onset of collision by a fold thrust belt beginning to rise in the position occupied today by the high and lesser himalayan structural domains throughout the murree supergroup main petrographic parameters do not vary greatly and volcanic sedimentary low grade metasedimentary and ophiolitic detritus persisted until the early miocene indicating slow progressive growth of the chain only during the middle miocene when the highly metamorphosed rocks of the high himalaya were carried southward along the main central thrust mct the mountain range began to rise to dramatic heights and huge amounts of detritus started to feed the siwalik foreland basin sandstones and the remnant ocean turbidites of the indus and bengal fans

paleocene latitude of the kohistan ladakh arc indicates multistage india eurasia collision we report paleomagnetic data showing that an intraoceanic trans tethyan subduction zone existed south of the eurasian continent and north of the indian subcontinent until at least paleocene time this system was active between 66 and 62 ma at a paleolatitude of 8 1 5 6 n placing it 600 2 300 km south of the contemporaneous eurasian margin the first ophiolite obductions onto the northern indian margin also occurred at this time demonstrating that collision was a multistage process involving at least two subduction systems collisional events began with collision of india and the trans tethyan subduction zone in late cretaceous to early paleocene time followed by the collision of india plus trans tethyan ophiolites with eurasia in mid eocene time these data constrain the total postcollisional convergence across the india eurasia convergent zone to 1 350 2 150 km and limit the north south extent of northwestern greater india to 900 km these results have broad implications for how collisional processes may affect plate reconfigurations global climate and biodiversity

paleogene carbonate microfacies and sandstone provenance gamba area south tibet stratigraphic response to initial india asia continental collision abstract the paleogene marine strata in the gamba area of south tibet comprise carbonates of the zongpu formation and siliciclastic rocks of the enba and zhaguo formations documenting the final stages of marine deposition in the tethyan himalaya the 350 m thick zongpu formation was dated as late danian to ypresian based on larger benthic foraminifers thirteen distinct microfacies identify three sedimentary environments mudstone wackestone with udoteacean algae bioclastic peloidal packstone packstone with rotaliids and green algae floatstone with alveolina and orbitolites were deposited in restricted lagoonal environments bioclastic packstone and grainstone with rotaliids were deposited in high energy shoal environments floatstones with nummulitids or alveolinids were deposited in shallow open marine environments the zongpu formation was accumulated on a carbonate ramp it documents two deepening upward sequences separated by an unconformity corresponding to the palaeocene eocene boundary and marked by a conglomerate with limestone clasts the overlying enba formation comprises greenish grey calcareous shales intercalated with litho quartzose sandstones in the upper part and capped by subaerial litho quartzose red beds of the zhaguo formation petrographic analysis detrital zircon geochronology and hf isotopic data indicate that detritus in the enba and zhaguo formations deposited on the indian passive margin was derived from the asian active margin in the north these clastic units were thus deposited after the onset of the india asia continental collision in the early himalayan foreland basin major lithological and paleoenvironmental changes occurred at three stratigraphic levels the jidula zongpu boundary 62 ma the paleocene eocene boundary 56 ma and the zongpu enba boundary 51 ma our provenance study confirms that the india asia collision was already under way during the deposition of the enba member i e by 51 ma and along with facies analysis and general palaeogeographic considerations indicates that neo tethys was still wide open during the early middle paleocene it is thus argued consistently with previous studies that the paleocene eocene disconformity documented in the gamba area as in the northwestern tethyan himalaya is likely to record flexural uplift consequent to initial underthrusting of the indian continental margin beneath asia at or just a little earlier than 56 ma

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

from static to dynamic provenance analysis sedimentary petrology upgraded abstract the classical approach to sandstone petrology established in the golden years of plate tectonics and based on the axiom that detrital modes of sandstone suites primarily reflect the different tectonic settings of provenance terranes has represented a benchmark for decades the composition of sand and sandstone however simply provides us with a distorted image of the lithological structure of source terranes and gives us little clue whether they are allochthonous or autochthonous orogenic or anorogenic young or old what we may able to see reflected in detrital modes is the nature of source terranes continental arc oceanic and the tectonostratigraphic level reached by erosion in space and time the proposed new approach to the petrology of sand and sandstone 1 starts with a simple classification scheme circulated since the 1960s which is purely descriptive objective and free of ill defined ambiguous terms and 2 focuses on the nature and tectonostratigraphic level of source terranes further steps are essential to upgrade provenance analysis acquiring knowledge from modern settings is needed to properly identify and wherever possible correct for physical and chemical processes introducing environmental and diagenetic bias and thus address nature s complexities with adequate conceptual tools equally important is the integration of multiple techniques ideally including bulk sediment multi mineral and single mineral methods bulk sediment petrography remains the fundamental approach that allows us to capture the most precious source of direct provenance information represented by the mineralogy and texture of rock fragments bulk sediment geochemistry applicable also to silt and clay carried in suspension is a superior method to check for hydraulic sorting chemical weathering and fertility of detrital minerals in different sediment sources detrital geochronology thermochronology and isotope geochemistry reveal the diverse time structures of source rocks and have become necessary complementary techniques in modern provenance analysis inferences on geodynamic processes need independent geological information and come last but if tackled properly they can lead us much farther than the standard label obtained by using triangular diagrams uncritically as if they were infallible oracles

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

latest cretaceous himalayan tectonics obduction collision or deccan related uplift abstract diverging interpretations and incompatible scenarios have been proposed for the early stages of himalayan history numerous researchers have postulated that northern india was involved in ophiolite obduction arc continent or continent continent collision during the late cretaceous or early paleocene but firm geological evidence was never produced in this article we argue against orogenic events predating the late paleocene when the neotethys ocean was still open the tethys himalayan sedimentary record testifies to anorogenic evolution primarily controlled by dynamic uplift of the passive margin prior to the massive outburst of deccan lavas and eventually followed by thermal subsidence major stratigraphic gaps in pelagic sediments suggest that such tectono magmatic episode started to affect the base of the indian plate in the campanian or possibly even in the santonian 10 to 20 ma before the climax of deccan flood basalt eruptions the abrupt increase in siliciclastic supply and accumulation rates recorded in sedimentary basins all around the indian subcontinent during the maastrichtian was followed by progradation of coastal quartzarenites along the northern indian margin in the early paleocene sandstones derived from the rejuvenated craton and uplifted inner continental margin in the south are dominantly but not exclusively quartzose felsitic volcanic rock fragments and cr spinels many of which with the same geochemical fingerprint as deccan spinels and newly found throughout the maastrichtian to danian succession resisted the combined effect of subequatorial weathering and subsequent diagenesis and testify that detritus from deccan basalts reached the indian passive margin as far as south tibet at the close of the early paleocene india drifted away from the seychelles block and thermal subsidence led to widespread carbonate deposition along the tethys himalaya this article illustrates how mega events of magmatic upwelling followed by lithospheric cooling may control passive margin sedimentation and stratigraphic patterns as occurred in northern india first in the early cretaceous and next in the latest cretaceous paleocene

zircon u pb and hf isotope constraints on the mesozoic tectonics and crustal evolution of southern tibet the first in situ hf and u pb isotope analyses of zircon separates from mesozoic granites in southern tibet identify a significant previously unknown stage of magmatism igneous zircons n 34 from a granite within the gangdese batholith show a weighted mean 206 pb 238 u age of 188 1 1 4 ma and e hf t the parts in 10 4 deviation of initial hf isotope ratios between the zircon sample and the chondritic reservoir values between 10 4 and 16 8 suggesting predominantly early jurassic intrusive activity with a juvenile mantle contribution of 40 inherited zircons from two cretaceous s type granites in the northern magmatic belt 23 delineate a slightly older 206 pb 238 u age cluster between 188 and 210 ma these zircons have e hf t values from 3 9 to 13 7 yielding crustal hf model ages from ca 1 4 to 2 1 ga suggesting a major episode of crustal growth in proterozoic time and remelting of this crust in early jurassic time combining these with literature data we interpret the jurassic gangdese magmatism as an early product of the neo tethyan subduction that played a long lasting role in the tectonic evolution of southern tibet prior to the india asia collision

paleogene volcanism in central afghanistan possible far field effect of the india eurasia collision abstract a volcanic sedimentary succession of paleogene age is exposed in isolated patches at the southern margin of the tajik block in the ghor province of central afghanistan the volcanic rocks range from basalts and andesites to dacites including adakites they are intercalated with sedimentary rocks deposited in shallow marine environments dated biostratigraphically as paleocene eocene this age corresponds to the age of the asy b d andesites located in the western ghor province estimated by the 40ar 39ar method as 54 ma the magmatism post dates the cimmerian collision between the tajik block including the band e bayan block and the farah rod block located to the south while the investigated volcanic rocks apparently bear geochemical signatures typical to an active continental margin environment it is presumed that the magmatism was related to rifting processes most likely initiated by far field tectonics caused by the terminal collision of the indian plate with eurasia najman et al 2017 this event led to the dextral movement of the farah rod block particularly along hari rod herat fault system resulting in the development of a transtensional regime in the proximal southern margin of the tajik block and giving rise to a rift basin where marine sediments were interbedded with pillow lavas intruded by sheeted dyke series

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

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

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

the palung granite himalaya high resolution upb systematics in zircon and monazite abstract u pb analyses of fractions of zircon and monazite 3 8 grains each and of single zircon grains resolve a lower ordovician age of 470 4m y for the palung granite which occurs in the high himalayan nappes south of kathmandu its thrusting during the alpine orogeny under lower greenschist facies conditions did not affect the u pb systems in zircon and monazite the granite crystallized from a magma which was mainly generated by anatexis of precambrian continental crust the magma was heterogeneous with respect to primary ages and or metamorphic histories of the magma source rocks this indicates either a derivation from meta sediments or an intense mixing of different crustally derived magmas the genesis of the palung granite is possibly related to an orogeny which affected the indian shield in lower palaeozoic times the detected inherited radiogenic lead in the palung zircons occurs in perfectly homogeneous transparent crystals i e this radiogenic excess lead is not related to the presence of old microscopically visible overgrown zircon cores the minimum ages of the inherited lead components range from about 800 to 1700 m y

dating protracted fault activities microstructures microchemistry and geochronology of the vaikrita thrust main central thrust zone garhwal himalaya nw india

u pb zircon ages from the spontang ophiolite ladakh himalaya the spontang ophiolite in the ladakh himalaya consist of a thrust sheet of upper mantle and oceanic crustal rocks obducted onto the northern passive continental margin of india during the late cretaceous precise isotopic ages of himalayan ophiolites are presently unavailable u pb dating of zircons from a dioritic segregation in the high level gabbros of the spontang ophiolite shows that the complex formed at 177 1 ma mid jurassic and we suggest that it represents a fragment of neo tethyan oceanic crust this jurassic age contrasts with late cretaceous ages 91 95 ma previously reported for the formation of the troodos and oman ophiolite complexes further west along the neo tethyan suture zone and also predates the early to mid cretaceous masirah ophiolite c 150 ma and its alkaline volcanic seamounts 115 125 ma an andesitic rock from an arc sequence overlying the spontang ophiolite was also dated using as 88 5 ma this late cretaceous age constrains the minimum age of initiation of subduction beneath the spontang ophiolite the complex was emplaced during the turonian maastrictian some 80 ma after its formation when the indian continental margin collided with a cretaceous arc about 25 ma before the india asia collision the lack of a sub ophiolite metamorphic sheet beneath the spontang mantle sequence may be explained by the fact that the ophiolite was old and cold at the time of obduction

petrochronology of himalayan ultrahigh pressure eclogite the timing and nature of the india asia collision earth s largest ongoing continent continent collisional orogen are unclear ultrahigh pressure metamorphism of indian continental margin rocks is used as a proxy for initial collision because it indicates subduction of india records of this metamorphism are preserved only at kaghan valley pakistan and tso morari ladakh india separated by 500 km and having published ages of peak pressure of 46 2 0 7 ma and 53 51 ma respectively the apparent 6 m y age difference may refl ect multiple subduction events a large promontory along the former indian margin or inadequate constraints on the time of peak pressure recrystallization at tso morari we present 108 coupled in situ u th pb and rare earth element ree analyses of zircons in two tso morari eclogites to obtain age and petrologic information the ages range from ca 53 ma to 37 ma and peak at ca 47 43 ma flat heavy ree slopes and the absence of an eu anomaly are compatible with eclogite facies zircon re crystallization this re crystallization probably occurred at ultrahigh pressure because 64 of the analyses are from zircon included in ultrahigh pressure garnet and omphacite these results are consistent with those from kaghan valley and suggest that a single protracted ultrahigh pressure metamorphic event occurred contemporaneously across much of the orogen following initial contact of the indian and asian continents at ca 51 ma or later

the zedong window a record of superposed tertiary convergence in southeastern tibet determining the timing magnitude and location of deformation due to the indo asian collision is widely acknowledged as an important step in understanding how the lithosphere responds during continental collision a puzzling result of geological investigations of the lhasa block over the past 2 decades has been the apparent lack of significant tertiary deformation there perhaps the most important structural feature of the lhasa block is the south directed gangdese thrust system which developed along its southern edge the thrust system which separates the andean type batholith of southern asia from rocks of indian affinity is obscured at most locations across southeastern tibet by back thrusts of the younger north directed renbu zedong thrust system the best documented site where both thrusts are exposed occurs near zedong zedong window systematic geochronologic analyses were conducted in this area u pb zircon dating of three samples of a synkinematically to postkinematically deformed hanging wall granitoid the yaja granodiorite cut by the gangdese thrust indicates a crystallization age of 30 4 0 4 ma 2 thus placing an upper bound on the initiation of the thrust u pb zircon dating of granitoid samples structurally higher in the gangdese hanging wall yields emplacement ages of 42 5 1 0 ma and 48 9 0 8 ma 2 similar to other magmatic complexes within the gangdese arc geochemical results are consistent with these plutons forming in the same environment as precollisional intrusions within the gangdese batholith suggesting a significant post collisional input of juvenile heat the 40ar 39ar thermochronology of samples from a vertical section through the hanging wall within the yaja granodiorite coupled with results of a numerical thermal model indicate an average slip rate along the gangdese thrust of 7 mm yr between 30 and 23 ma and a minimum displacement of 50 km farther east in the zedong window thermal effects produced by later north directed thrust sheets of the renbu zedong system appear to have obscured thermal history signatures in the gangdese hanging wall related to earlier south directed thrusting thermochronological results from this region indicate that thermal overprinting related to the north directed thrusting occurred between 25 and 10 ma consistent with previous estimates

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

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

the tethyan himalayan detrital record shows that india asia terminal collision occurred by 54 ma in the western himalaya the himalayan orogen is a type example of continent continent collision knowledge of the timing of india asia collision is critical to the calculation of the amount of convergence that must have been accommodated and thus to models of crustal deformation sedimentary rocks on the indian plate near the suture zone can be used to constrain the time of collision by determining first evidence of asian derived material deposited on the indian plate however in the himalaya for this approach to be applied successfully it is necessary to be able to distinguish between asian detritus and detritus from oceanic island arcs that may have collided with india prior to india asia collision zircons from the indian plate asian plate and kohistan ladakh island arc can be distinguished based on their u pb ages combined with hf signatures we undertook a provenance study of the youngest detrital sedimentary rocks of the tethyan himalaya of the indian plate in the western himalaya we show that zircons of asian affinity were deposited on the indian plate at 54 ma we thus constrain terminal india asia collision when both sutures north and south of the kohistan ladakh island arc were closed to have occurred in the western himalaya by 54 ma

greater india basin hypothesis and a two stage cenozoic collision between india and asia cenozoic convergence between the indian and asian plates pro duced the archetypical continental collision zone comprising the himalaya mountain belt and the tibetan plateau how and where india asia convergence was accommodated after collision at or be fore 52 ma remains a long standing controversy since 52 ma the two plates have converged up to 3 600 35 km yet the upper crustal shortening documented from the geological record of asia and the himalaya is up to approximately 2 350 km less here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic indian lithosphere within the himalaya be tween approximately 50 and 25 ma paleomagnetic data show that this extended continental and oceanic greater india promontory resulted from 2 675 700 km of north south extension between 120 and 70 ma accommodated between the tibetan himalaya and cratonic india we suggest that the approximately 50 ma india asia collision was a collision of a tibetan himalayan microconti nent with asia followed by subduction of the largely oceanic greater india basin along a subduction zone at the location of the greater himalaya the hard india asia collision with thicker and contiguous indian continental lithosphere occurred around 25 20 ma this hard collision is coincident with far field deforma tion in central asia and rapid exhumation of greater himalaya crys talline rocks and may be linked to intensification of the asian monsoon system this two stage collision between india and asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography

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

multiple mantle sources during island arc magmatism u pb and hf isotopic evidence from the kohistan arc complex pakistan this paper presents high precision u pb ages and initial hf isotopic compositions of zircon from mafic to felsic rocks of the kohistan arc complex pakistan three magmatic pulses tapping geochemically different reservoirs are distinguished partial melting of mantle with morb type isotopic characteristics generated 99 92 ma old magmas plutonism around 85 ma tapped a more fertile mantle source most likely consisting of a 600 ma old metasomatically enriched mantle or of mantle contaminated by an old sedimentary component 82 ma old felsic peraluminous dykes have morb type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc the isotopic results demonstrate several and rather rapid changes in melt source region during arc development they also show that there was subordinate continental influence and negligible importance of slab components for the hf budget during the generation of the kohistan arc complex

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

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

sedimentology of the indus group ladakh northern india implications for the timing of initiation of the palaeo indus river the upper reaches of the indus river form a longitudinal network that drains a large portion of the western himalaya it plays an important role as a sediment routing system feeding the indus delta and submarine fan and has played a controlling role in the denudational history of the western himalaya given the rivers long term significance its timing of initiation remains poorly constrained the facies palaeocurrents and provenance of the post early eocene indus group preserved along the upper reaches of the modern indus reveal a history of fluvial deltaic and deep water sedimentation in an intermontane basin dominated by internal drainage hence the indus group is not considered to represent the deposits of a palaeo indus river as previously thought illite crystallinity values and apatite fission track dating of the indus group suggest that the succession was buried to temperatures of 155 280 c and that unroofing started in early miocene times and proceeded at 0 1 0 4 mm a 1 to the present the youngest sedimentary rocks preserved along the indus basin are early miocene in age from the tectonostratigraphically equivalent deposits around kargil to the west of the study area the transition from sediment accumulation to erosional unroofing in early miocene times coincides with accelerated regional unroofing of the high himalayas to the south and the initiation of the indus delta submarine fan to the west differential uplift between the northward thrusting of the zanskar and indus sedimentary succession against the undeformed ladakh batholith provides a mechanism for post early miocene initiation of a major longitudinal river hence early miocene times is believed to represent the earliest possible age of initiation of the palaeo indus river following this course

geochemical investigation of early cretaceous igneous rocks along an east west traverse throughout the central lhasa terrane tibet article i nfo bulk rock major and trace element sr nd isotope zircon u pb and hf isotope data are reported for early cretaceous igneous rocks sampled along an east west traverse through the central lhasa subterrane e80 00 e89 in southern tibet these results offer new insights into the pre cenozoic geology and tectonomagmatic evolution of the lhasa terrane and provide boundary conditions for the origin and evolution of the tibetan plateau our new data together with data from the literature indicate that the early cretaceous magmatism in the central lhasa subterrane lasted for a long period 143 102 ma with a magmatic flare up at 110 ma the latter is accompanied by mafic magmatism in this terrane the silicic rocks are metaluminous to peraluminous and enrichedinrb th and u and depleted inba nb ta sr p and ti withvarying initial 87

leucogranite geochronological constraints on the termination of the south tibetan detachment in eastern himalaya abstract the south tibetan detachment system stds developed between the very low grade tethyan himalayan sequence ths and the high grade metamorphic greater himalayan sequence ghs over an along strike distance exceeding 2000 km within the himalayan orogen motion along the stds has been associated with the exhumation of the ghs and the uplift of the himalayan mountains geological field mapping and u th pb geochronological analyses were performed to trace and date the stds in the yadong region of southern tibet where it is a top to the north shear zone juxtaposing the yadong klippe of the ths with the high grade ghs this shear zone is intruded by multiple generations of leucogranites emplaced mainly at ca 23 ma ca 20 18 ma and ca 17 16 ma the undeformed textures of the leucogranites and their cross cutting relationships with the shear zone indicate that ductile motion along the stds terminated by ca 20 ma this is largely consistent with the deformation history of the stds in central and western himalaya the termination of shearing along the stds during the early miocene occurred well before the rapid cooling of the ghs during the middle miocene suggesting that exhumation and decompression of the ghs was still ongoing after the cessation of motion along the stds