hydrothermal source of radiogenic sr to himalayan rivers 1 k 1 and cl 2 all of which are high in the hydrothermal waters cation concentrations decrease along the lesser himalayan reach of the river hot spring dissolved co2 has a d 13 c value to 15 9 indicating that metamorphic decarbonation reactions contribute co2 to the fluids hydrothermal co2 is partially neutralized in high temperature weathering reactions which generate alkalinity and yield abundant radiogenic sr radiogenic hydrothermal carbonate can form from these solutions and later weather releasing silicate sr but imparting carbonate characteristics to the overall water chemistry

effect of differential stress on strontium partitioning in calcite abstract strontium content of calcite has been used to aid in the interpretation of diagenesis of carbonate rocks however the distribution coefficient for strontium partitioning between calcite and solution kdsr ca is subject to both kinetic and thermodynamic factors that are incompletely understood the effect of stress which may involve both of these factors on the partitioning of trace element cations in the carbonate lattice has not previously been investigated aragonite to calcite transformation may occur under axial stress burial conditions if aragonite rich sediments escape near surface diagenetic alteration the effect of stress on kdsr ca during aragonite to calcite conversion was investigated through experimental compaction studies experiments investigated partitioning behavior under conditions of purely hydrostatic fluid pressure surrounding growing calcite crystals changes in hydrostatic pressure up to 35 mpa isothermal had little or no effect on the partitioning of strontium into calcite varying solution sr ca ratios at constant temperature likewise had no effect on the distribution coefficient hydrostatic experiments also investigated the temperature dependence of partitioning experimental data indicate that kdsr ca at stp is about 0 028 an experimental design was also constructed to test whether differential stress affects the kdsr ca value a compaction apparatus was used to generate an effective stress of over 5 mpa simulating lithostatic burial load at approximately 240 m temperature was held constant during experimental compaction runs data from compaction experiments show an order of magnitude depression of kdsr ca with increasing effective stress in the range from 0 to 5 35 mpa these empirical results may aid in the interpretation of low sr limestones in the geologic record

new geochemical support for mixing zone dolomitization at golden grove barbados dolomite occurs in the golden grove reef terrace of late pleistocene age in southeastern barbados where fore reef lithologies have been partially to completely dolomitized interpretation of the possible modes of formation of this dolomite has been a subject of disagreement for over a decade among the points of contention are the timing of deposition dolomitization and dolomite cement precipitation and the relationship of replacement dolomite with dolomite cement data from this study indicate that dolomitization occurred during a single relative sea level fall following reef development at marine oxygen isotope stage 7 3 at approximately 216 ka replacement dolomitization affected both micritic matrix and skeletal grains during or after replacement dolomitization dolomite and calcite cements filled primary and secondary pores the cement paragenesis comprises early dolomite cement complexly banded cements of alternating calcite and dolomite late dolomite cement of near stoichiometric composition and a final phase of blocky calcite cement replacement dolomitization and cement precipitation represent a continuum of processes resulting from progressive modification of diagenetic fluids stable carbon and oxygen isotope and strontium elemental compositions of replacive dolomite dolomite cements and calcite cements indicate that dolomitization occurred in a mixing zone between marine and meteoric groundwaters occupying the reef terrace shortly after deposition dolomite oxygen isotope values range from 0 18 to 3 85 pdb and become progressively more depleted throughout the paragenesis indicating a greater influence of meteoric water through time remarkably depleted carbon isotope compositions for both replacement dolomite and dolomite cement 9 53 to 23 04 pdb originated from oxidation of thermogenic methane advected from the underlying accretionary complex methane was oxidized in marine waters that subsequently mixed with meteoric waters as evidenced by a progressive enrichment in carbon isotope composition throughout the paragenesis dolomite strontium contents are substantially elevated above those expected for marine dolomitization ranging from 640 to 1650 ppm and increasing throughout the paragenesis meteoric water provided the excess strontium as aragonite to calcite transformation in the exposed reef terrace increased the fluid sr ca ratio the continuum of geochemical compositions between the replacement dolomite and dolomite cement argues for their genetic association these new data provide additional support to the mixing zone interpretation for golden grove and that the model of mixing zone dolomitization remains viable

palaeomagnetism of cretaceous to tertiary sediments from southern tibet evidence for the extent of the northern margin of india prior to the collision with eurasia abstract palaeomagnetic studies have been carried out on mid cretaceous to latest palaeocene sediments from the tethyan himalaya on the northern margin of the indian plate near the localities of gamba 28 3 n 88 5 e and duela 28 0 n 89 2 e in southern tibet a total of 61 sites more than 700 cores have been sampled mainly from limestones zongshan formation jidula formation member ii zongpu formation sandstones jidula formation member iii and graywackes gamba group member ii with ages well defined from detailed lithological and biostratigraphic analyses carriers of characteristic remanences are magnetite in limestones and graywackes and hematite in sandstones reliable palaeodirections were obtained from 35 sites 356 specimens positive fold tests antiparallel normal and reverse polarities a northward trend of the palaeolatitudes with decreasing age and absence of any metamorphic overprint indicate a primary origin for the characteristic remanences the results have been compared with expected palaeodirections according to available data for the indian subcontinent based on its present day geometry the late maastrichtian sites fourteen sites 156 specimens and the middle late palaeocene sites fourteen sites 113 specimens yield palaeolatitudes of 5 7 s and 4 0 n for the sampling localities in southern tibet respectively these palaeolatitudes are much further north than expected and imply that crustal shortening between the tethyan himalaya and the indian shield since the time of india eurasia collision has occurred on the order of 1500 km at the longitude of gamba duela comparison of our observed palaeolatitudes with palaeolatitudes for the lhasa block during cretaceous and palaeocene times indicate that initial contact of the northern indian margin with the lhasa block was already established at 65 60 ma with suturing completed at about 55 50 ma

neogene marine isotopic evolution and the erosion of lesser himalayan strata implications for cenozoic tectonic history abstract an extensive northward deepening blanket of neoproterozoic and cambrian sedimentary rocks once extended from the himalayan margin far onto the indian craton cambrian deposits of this upper lesser himalayan succession which include deposits of the outer lesser himalaya tectonic unit are enriched in radiogenic 187os they make up part of a proximal marine facies belt that extends onto the craton and along strike from india to pakistan by contrast age equivalent facies in the tethyan himalaya are more distal in nature neoproterozoic to cambrian strata of the upper lesser himalayan succession are now missing in much of the lesser himalaya with their erosion exposing older precambrian lesser himalayan strata we suggest that exhumation and weathering of the upper lesser himalaya and related strata caused dramatic changes in the 187os 188os and 87sr 86sr neogene record of seawater starting at 16 ma first order estimates for the volume of upper himalayan strata as well as the volume of all lh rock eroded since this time and geochemical box modeling support this idea exhumation at 16 ma is a fundamental event in the evolution of the himalayan orogeny and the geochemical evolution of the oceans and will be a critical part of the construction of future models of himalayan thrust belt evolution

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

origin of strontium and calcium in pedogenic needle fibre calcite nfc abstract strontium sr and calcium ca isotopic compositions and sr ca ratios have been analysed in different fractions of pedogenic needle fibre calcite nfc from the swiss jura mountains villiers neuch tel switzerland in order to determine their ca sources and to investigate the potential role of fungi in the origin of nfc 87sr 86sr ratios have been measured to trace the ca trapped within different pedogenic carbonate this ratio was compared for previously identified microscopic morphological groups of nfc the bulk soil fine earth

biotic and inorganic control on travertine deposition at bullicame 3 spring viterbo italy a multidisciplinary approach abstract a multidisciplinary characterization of an active thermal spring in central italy has been undertaken with the aim of i ascertaining whether microbiological activity plays a relevant role in hot depositing travertines and ii establishing an experimental protocol able to identify similar effects in fossil travertines water gas and travertine samples were investigated by chemical icp ms sem eds physical dta dtg isotopic 18o d and 13c mineralogical xrpd and spectroscopic epr techniques twenty four samples three for each phase were collected every 5 c temperature drop along a 100 m long artificial channel near viterbo bullicame 3 latium central italy a microbiological characterization was carried out in parallel sampling the channel every 10 c temperature drop the bullicame 3 system is revealed to be composed of two markedly different subsystems a water gas interface where a kinetically fast exchange allows equilibrium of components both in water and in gases a solid water interface where travertine precipitation occurs influenced by microbiological activity a peculiar lattice shrinking of calcite was identified as well as an anomalous value of the zero field splitting parameter from the epr measurements the interpretation of these anomalies is confirmed by the identification of calcifying cyanobacteria throughout the channel path our results point out that microbiological activity can play a significant role in travertine deposition from hot springs furthermore the proposed approach representing a tool to identify crystal chemical remnants of past microbiological activity could be applicable to fossil travertines

mantle derived spinel lherzolite xenoliths from the deccan volcanic province india implications for the thermal structure of the lithosphere underlying the deccan traps abstract petrography mineral and host rock chemistry of the mantle derived spinel lherzolite xenoliths in the nephelinites of kutch a late variant of the deccan traps province india are reported the xenoliths register equilibration temperatures between 920 70 c and 1060 50 c and an ascent time between 19 and 168 days representing a palaeogeotherm of minimum heat flow between 60 and 70 mw m 2 the xenoliths possibly came from the oceanic lithosphere under the deccan field following the cretaceous eocene fragmentation of gondwanaland

paleocene eocene foreland basin evolution in the himalaya of southern tibet and nepal implications for the age of initial india asia collision siliciclastic sedimentary rocks derived from the southern lhasa terrane sitting depositionally upon rocks of the northern indian passive continental margin provide an estimate of the age of initial contact between the continental parts of the indian and asian plates we report sedimentological sedimentary petrological and geochronological data from upper cretaceous paleocene strata in the sangdanlin section located along the southern flank of the indus yarlung suture zone in southern tibet this is probably the most proximal and therefore the oldest record of the india asia collision these strata were deposited by high density turbidity currents or concentrated density flows and suspension settling of pelagic biogenic debris in a deep marine setting an abrupt change from quartz arenitic to feldspatholithic sandstone compositions marks the transition from indian to asian sediment provenance the abrupt compositional change is accompanied by changes in u pb ages of detrital zircons diagnostic of a sediment provenance reversal from indian to asian sources the timing of the transition is bracketed between 60 ma and 58 5 0 6 ma by detrital zircon u pb ages and zircon u pb ages from a tuffaceous bed in the upper part of the section in the context of a palinspastically restored regional paleogeographic framework data from the sangdanlin section combined with previously published data from the northern tethyan himalaya and the frontal nepalese lesser himalaya and subhimalaya suggest that a flexural wave migrated 1300 km southward across what is now the himalayan thrust belt from paleocene time to the present

processes controlling sr in surface and ground waters of tertiary tholeiitic flood basalts in northern iceland strontium concentrations of 253 natural water samples from skagafjordur a tertiary tholeiitic flood basalt region in northern iceland range between 0 10 and 28 ppb surface environments rivers lakes and peat soil waters include the whole range of observed sr concentrations whereas the sr concentrations of ground waters are in most cases 3 5 ppb concentrations of sr derived from basalt dissolution i e rock derived sr in waters of rivers and lakes exhibit a near linear correlation with the concentration of rock derived ca with a median molar ca sr ratio of 1350 this systematic correlation suggests that ca and sr concentrations are controlled by weathering processes i e the extent of dissolution of the basalt the relative mobility of sr during weathering in skagafjordur is approximately half that of ca which is consistent with observed relative mobilities of these elements elsewhere in iceland and in other basaltic regions peat soil waters commonly have lower concentrations of sr and higher ca concentrations than rivers and lakes and molar ratios of rock derived ca to sr in peat soil waters exhibit no systematic pattern in several cases calculated concentrations of rock derived sr in peat soil waters yield negative values suggesting a mineralogic sink for sr in these waters the low sr concentrations in cold and thermal ground waters 3 5 ppb suggest mineralogic control over sr in the ground water systems precipitation of secondary sr minerals such as strontianite and celestite is ruled out as the ground waters are understaturated with respect to these minerals ground waters are characterized by high ca sr molar ratios 5000 compared to bedrock ca sr ratio of 730 suggesting that sr is being preferentially incorporated relative to ca into secondary minerals the secondary minerals present in the bedrock in skagafjordur that can preferentially incorporate sr include zeolites such as heulandite chabazite and thomsonite and smectite ion exchange calculations demonstrate that activities of sr2 and ca2 in ground water solutions in skagafjordur are consistent with ion exchange equilibria between these waters and heulandite from other tertiary basalts in iceland suggesting that this mineral may play an important role in controlling the concentration of sr in the skagafjordur ground waters incorporation of sr into calcite cannot explain the observed high ca sr ratios of the skagafjordur ground waters because calcite when precipitating only admits limited amounts of sr aragonite is not considered a likely candidate either because it has only very slight preference for sr over ca and ground waters above 40 c are undersaturated with respect to this phase however predicted sr content of calcite in equilibrium with the skagafjordur ground waters 0 5 83 ppm sr is in good agreement with measured sr content of this mineral in tertiary basalts elsewhere in iceland 0 1 63 ppm suggesting that the skagafjordur ground waters can be used as analogues for tertiary crustal solutions involved in the zeolite facies metamorphism of the icelandic crust

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

geochemical record of holocene to recent sedimentation on the western indus continental shelf arabian sea 1 we present a multiproxy geochemical analysis of two cores recovered from the indus shelf spanning the early holocene to recent 14 ka indus 23 is located close to the modern indus river while indus 10 is positioned 100 km further west the holocene transgression at indus 10 was over a surface that was strongly weathered during the last glacial sea level lowstand lower holocene sediments at indus 10 have higherendvalues compared to those at the river mouth indicating some sediment supply from the makran coast either during the deposition or via reworking of older sediments outcropping on the shelf sediment transport from makran occurred during transgressive intervals when sea level crossed the mid shelf the sediment flux from non indus sources to indus 10 peaked between 11 ka and 8 ka a hiatus at indus 23 from 8 ka until 1 3 ka indicates non deposition or erosion of existing indus shelf sequences higherendvalues seen on the shelf compared to the delta imply reworking of older delta sediments in building holocene clinoforms chemical index of alteration cia mg al and sr isotopes are all affected by erosion of detrital carbonate which reduced through the holocene k al data suggest that silicate weathering peaked ca 4 6 ka and was higher at indus 10 compared to indus 23 fine grained sediments that make up the shelf have geochemical signatures that are different from the coarser grained bulk sediments measured in the delta plain the indus shelf data highlight the complexity of reconstructing records of continental erosion and provenance in marine settings

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

controls on sr isotopic evolution in lacustrine systems eocene green river formation wyoming abstract strontium isotopes from lacustrine carbonates record detailed weathering histories of exposed bedrocks and thus are potentially useful for understanding interactions between tectonics and climate that may be driven by local or regional factors in basin scale hydrologic systems we combine extensive 87 sr 86 sr and 18 o datasets from the green river formation in order to identify environmental factors driving the evolution of sr concentration and isotopic composition in lacustrine systems through the use of sr mass balance modeling two models are developed the first tests the effect of drainage capture that drove a constant volume lake from balance filled to overfilled conditions and is applied to the laney member of the green river formation the second model focuses on lacustrine evolution in response to changing the concentration composition and mass of water influx in a variable size sr reservoir lake this model is applied to the wilkins peak member of the green river formation 87 sr 86 sr ratios are correlated with 18 o values only during the laney member when both are readily explained by a common forcing mechanism drainage capture modeling of sr isotope compositions and concentrations indicates a short residence time for sr 10 3 10 4 years or less in both balance overfilled and underfilled phases of the green river formation lacustrine system this in turn suggests that paleo lacustrine sediments in most lakes can preserve sr isotope records with high resolution 10 2 years timescales rates of sr sequestration in carbonate are shown to have a strong influence on lacustrine sr concentration and high sr concentrations of lacustrine carbonate consistent with high salinity are observed in the underfilled wilkins peak member and the balance filled tipton and lower laney members in the laney member 87 sr 86 sr mass balance modeling results provide additional support for previous interpretations that the introduction of a large drainage system produced an isotopic shift across the lower laclede upper laclede boundary major drainage reorganization is not required to drive high variability in 87 sr 86 sr ratios however modeling shows that variability in 87 sr 86 sr ratios of 0 004 observed in the wilkins peak member can be explained by change in the characteristics of intrabasinal water sources during highstand vs lowstand conditions

constraints on the collision and the pre collision tectonic configuration between india and asia from detrital geochronology thermochronology and geochemistry studies in the lower indus basin pakistan abstract knowledge of the timing of india asia collision is a fundamental prerequisite for understanding the evolution of the himalayan tibetan orogen and its role in global climate oceanic chemistry and ecological evolution despite much active research the basic pre collision tectonic configuration and the timing of terminal india asia suturing remain debated for example debates regarding when and how the intervening kohistan ladakh arc was sutured with india and asia still remain elusive some models propose the arc collided with asia at about 100 ma with india asia collision at ca 55 ma whilst a newer model proposed the arc s collision with india at 50 ma and subsequently with asia at 40 ma another example is the recent proposition that an oceanic greater india basin separated the tethyan himalaya microcontinent from the remaining indian plate until 20 25 ma with the consumption of this oceanic basin marking the final collision at this time these controversies relate to whether the commonly documented 50 ma contact represents the terminal india asia suturing or the amalgamation between various arcs or microcontinents with india or asia here we present an integrated provenance study of geochronology thermochronology and geochemistry on the late cretaceous pleistocene sediments from the lower indus basin on the indian plate the detrital zircon u pb and fission track data show a reversal in sediment source from a pure indian signature to increasing inputs from the suture zone and the asian plate between the middle paleocene and early oligocene the nd and sr isotopes narrow down this change to 50 ma by revealing input of asian detritus and the establishment of a nd sr isotopic pattern similar to the present day indus fan by 50 ma with no significant variations up section contrary to what might be expected if later major collisions had occurred our isotopic data indicate that greater india was occupied by a fluvial deltaic system analogous to the present day indus and named as the paleo indus which has been transporting asian detritus southward across the suture zone and kohistan ladakh arc since 50 ma suggesting no other ocean basins intervened between india and asia after this time in this region our data require that in the west the india asia collision were accomplished by 50 ma

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

acoustic distribution of discriminated micronektonic organisms from a bi frequency processing the case study of eastern kerguelen oceanic waters abstract despite its ecological importance micronekton remains one of the least investigated components of the open ocean ecosystems our main goal was to characterize micronektonic organisms using bi frequency acoustic data 38 and 120 khz by calibrating an algorithm tool that discriminates groups of scatterers in the top 300 m of the productive oceanic zone east of kerguelen islands indian sector of the southern ocean the bi frequency algorithm was calibrated from acoustic properties of mono specific biological samples collected with trawls thus allowing to discriminate three acoustic groups of micronekton i gas bearing sv 120 38 2 db and iii undetermined scatterers 1

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

timing of india asia collision geological biostratigraphic and palaeomagnetic constraints 1 a range of ages have been proposed for the timing of india asia collision the range to some extent reflects different definitions of collision and methods used to date it in this paper we discuss three approaches that have been used to constrain the time of collision the time of cessation of marine facies the time of the first arrival of asian detritus on the indian plate and the determination of the relative positions of india and asia through time in the qumiba sedimentary section located south of the yarlung tsangpo suture in tibet a previous work has dated marine facies at middle to late eocene by far the youngest marine sediments recorded in the region by contrast our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50 6 52 8 ma in broad agreement with the timing of cessation of marine facies elsewhere throughout the region double dating of detrital zircons from this formation by u pb and fission track methods indicates an asian contribution to the rocks thus documenting the time of arrival of asian material onto the indian plate at this time and hence constraining the time of india asia collision our reconstruction of the positions of india and asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early eocene we conclude the paper with a discussion on the viability of a recent assertion that collision between india and asia could not have occurred prior to 35 ma

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

testing the validity of nd isotopes as a provenance tool in southern tibet for constraining the initial india asia collision abstract sm nd isotopic systematics has been proven to be a powerful tool for investigating the source provenance and tectonic significance of sedimentary rocks here i report the nd isotopic compositions of mesozoic to paleogene siliciclastic sediments from southern tibet in an attempt to determine the temporal variations in their provenance the data reveal a shift in end 0 values of mesozoic strata in the tethyan himalaya varying from 16 3 to 12 7 in the jurassic to 8 1 to 3 7 in the cretaceous the less negative end 0 values of the cretaceous siliciclastic rocks indicate increasing input of a juvenile mantle component from the source region such a shift can be attributed to the early cretaceous mantle derived magmatism that was predominant in northern greater india this study indicates that there is a significant overlap in the end 0 values of rocks from the tethyan himalaya and lhasa block implying that nd isotopes may not be a good provenance proxy to constrain the initiation of the india asia collision such an inference is also evidenced by similar nd isotopic compositions between rocks from the bhainskati formation in the nepalese foreland basin sourced from the tethyan himalaya and the enba and zhaguo formations in southern tibet sourced from the lhasa block

provenance of the upper cretaceous eocene deep water sandstones in sangdanlin southern tibet constraints on the timing of initial india asia collision abstractthe first arrival of sedimentary material from asia onto the indian continental margin provides a minimum constraint on the timing of initial india asia collision a combination of petrology detrital cr spinel geochemistry and zircon u pb dating of the upper cretaceous to eocene deep water succession at the sangdanlin section southern tibet provides evidence for major provenance change within the strata the upper cretaceous paleocene denggang formation quartzarenites contain zircons with dominant proterozoic ordovician u pb ages with an additional age peak of early cretaceous which we interpret to be derived from the northern indian margin by contrast the lithic sandstones of the early to middle eocene sangdanlin and zheya formations are dominated by zircons younger than 200 ma showing one major peak at 80 125 ma and two subdominant peaks at 54 70 and 180 196 ma comparable to those from the gangdese magmatic arc cr spinels in the sangdanlin and zheya formations are abundant and char

age of initiation of collision between india and asia a review of stratigraphic data abstract the collision of india with asia is perhaps the most profound tectonic event to have occurred in past 100 ma it is responsible for the uplift of the himalayas and tibetan plateau and has been argued to have been responsible for geological geochemical and climatological consequences of global extent yet the age of initiation of this collision remains poorly constrained the literature is replete with estimates that range from the late cretaceous 65 ma to latest eocene

temperature dependence of the strontium distribution coefficient in calcite an experimental study from 408 degrees to 2008 degrees c and application to natural diagenetic calcites abstract the temperature dependence of sr coprecipitation with calcite was determined experimentally in solutions with sr ca ratios and ionic strengths closely resembling marine pore fluids aragoniteto calcite and dolomite to calcite transformations were conducted over a temperature range from 40 to 200 c temperature dependence of the distribution coefficient of strontium in calcite dcsr is significant dcsr in aragonite to calcite experiments varied from 0 046 at 40 c to 0 068 at 200 c dcsr in dolomite to calcite experiments varied from 0 034 at 40 c to 0 062 at 200 c experimental values of dcsr are somewhat dependent on the precursor phase the experimental results are applied to natural diagenetic and hydrothermal calcites recovered from the sediment covered middle valley part of the juan de fuca ridge spreading center ocean drilling program holes 857c and 858d low mg calcites from hole 858d have sr contents appropriate for their present day in situ temperatures and pore water sr values in contrast high mg calcites from hole 858d that precipitated from supersaturated pore waters at inferred high growth rates have elevated sr contents relative to calculated equilibrium values the sr contents of calcites from hole 857c are close to predicted equilibrium values in some instances but are substantially different in others deviations from predicted equilibrium sr contents especially in nodules are attributed to the formation of mixed generations of carbonate precipitating with increasing burial depths and temperatures through pore waters with variable sr composition