the new england batholith of eastern australia evidence of silicic magma mixing from zircon 176hf 177hf ratios abstract zircon hf isotopic data from six granite supersuites recognised in the new england batholith of eastern australia indicate that magma mixing is present in all plutons apart from the s type supersuites inherited zircons are rare to absent suggesting that initial melt temperatures were above zircon saturation for the m i and a type granites in all supersuites the range of zircon hf model ages calculated relative to arc mantle varies greatly with younger model ages somewhat less than the permian and triassic age of crystallisation and older model ages indicating derivation from source rocks that may be as old as neoproterozoic the older model ages are consistent with late precambrian rocks in the lower crust that may be elements of the lachlan fold belt underlying the new england fold belt whole rock 18 o and end values 87 sr 86 sr initial ratios sr i and oxidation state fe 2 o 3 feo are summarised for the five named supersuites and for a previously unnamed group of triassic plutons situated east of the main batholith for which we propose the name carrai supersuite supersuites with higher 18 o higher sr i lower 7 li and lower fe 2 o 3 feo ratios indicate a metasedimentary component input the pattern of zircon hf isotopic variation reflects the other isotopic and geochemical indicators closely the additional value being that it preserves a magmatic crystallisation record of hf isotopic variation that is a measure of magma mixing from magma generation to final crystallisation using the above criteria at least three distinct crustal components are considered necessary to explain the compositional and isotopic diversity within the batholith the crustal components indicated are 1 a metasedimentary component of carboniferous and devonian age for the hillgrove bundarra and uralla supersuites 2 a lower crustal k rich and sr rich i type component for the moonbi carrai and possibly uralla supersuites that could be as old as proterozoic and 3 a lower crustal k poor i type component of uncertain age for the clarence river supersuite in all supersuites there is strong evidence of an m type component based on the presence of zircons with high ehf values

new insights into the timing of the india asia collision from the paleogene quxia and jialazi formations of the xigaze forearc basin south tibet abstract the xigaze forearc basin provides information on subduction evolution and magmatic growth of the gangdese arc as well as on the india asia continental collision recently obtained sedimentological biostratigraphic petrographic geochemical and geochronological data on cretaceous to paleogene strata in the cuojiangding area zhongba county south tibet shed new light on the tectonic evolution of the southern margin of the lhasa block during closure of neotethys and initial collision with india the uppermost cretaceous padana and qubeiya formations deposited in deltaic to inner shelf environments and representing the final filling of the xigaze forearc basin were unconformably overlain by the quxia and jialazi formations deposited in fan delta environments during the paleocene earliest eocene petrographic data and u pb ages of detrital zircons document the progressive unroofing of the gangdese arc which remained the dominant source of detritus throughout the late cretaceous to paleogene detrital cr spinels in the quxia and jialazi formations are geochemically similar to those in cretaceous xigaze forearc strata but different from those hosted in yarlung zangbo ophiolites suggesting that the latter were not exposed to erosion in the considered time window sandstone petrography cr spinel geochemistry u pb age spectra and hf isotopic ratios of detrital zircons in the quxia and jialazi formations match those in paleogene sediments deposited on the distal sangdanlin and zheya formations and proximal indian margin enba and zhaguo formations suggesting that the quxia and jialazi formations documents syncollisional fan deltas deposited on top of the nascent himalayan orogenic belt in this scenario the onset of the india asia collision predates deposition of the quxia and jialazi formations and is thus constrained as younger than 66 ma and older than 58 ma

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

tectonic erosion of the peruvian forearc lima basin by subduction and nazca ridge collision 1 subsidence of lima basin part of the peruvian forearc is controlled by tectonic erosion by the subducting nazca plate multichannel seismic reflection data coupled with age and paleowater depth constraints derived from ocean drilling program odp coring now allow the rates of erosion to be reconstructed through time in trenchward locations the forearc has experienced limited recent relative uplift 700 850 m likely due to preferential basal erosion under the center of lima basin long term subsidence driven by basal tectonic erosion dominates and is fastest closest to the trench since 47 ma eocene up to 148 km of the plate margin have been lost at an average rate of up to 3 1 km myr 1 appoximately 110 km of that total appears to be lost since 11 ma implying much faster average rates of trench retreat 10 km myr 1 since collision of the nazca ridge with the lima basin at 11 ma although there is no clear subsidence event at odp site 679 during the time at which nazca ridge was subducting beneath this part of the forearc 4 11 ma the more trenchward odp sites 682 and 688 show significant deepening after 11 ma indicating that subduction of the ridge accelerates tectonic erosion long term rates of crustal erosion in the region of lima basin are greater than estimates of regional arc magmatic productivity implying that such margins are net sinks of continental crust

u pb zircon geochronology of major lithologic units in the eastern himalaya implications for the origin and assembly of himalayan rocks models for the origin and deformation of himalayan rocks are dependent upon geometric and age relationships between major units we present field mapping and u pb dating of igneous and detrital zircons that establish the lithostratigraphic architecture of the eastern himalaya revealing that 1 the south tibet detachment along the bhutan china border is a top to the north ductile shear zone 2 late triassic and early cretaceous sedimentary samples from the northern indian margin show a similar age range of detrital zircons from ca 3500 ma to ca 200 ma but the late triassic rocks are distinguished by a significant age cluster between ca 280 and ca 220 ma and a well defined age peak at ca 570 ma 3 an augen gneiss in the south tibet detachment shear zone in southeast tibet has a cambrian ordovician crystallization age 4 main central thrust hanging wall paragneiss and footwall quartzites from the far western arunachal himalaya share similar provenance and late proterozoic maximum depositional ages and 5 main central thrust footwall metagraywacke from the central western arunachal himalaya has a paleoproterozoic maximum depositional age indicated by a single prominent age peak of ca 1780 ma recent work in the eastern himalaya demonstrates that in the early middle miocene the himalayan crystalline core here was emplaced southward between two subhorizontal shear zones that merge to the south a proposed subsequent middle miocene brittle low angle normal fault accomplishing exhumation of these rocks along the range crest can be precluded because new and existing mapping demonstrates only a ductile shear zone here the ca 280 220 ma detrital zircons of the late triassic strata are derived from an arc developed along the northern margin of the lhasa terrane detritus from this arc was deposited on the northern margin of india during india lhasa rifting along strike heterogeneity in main central thrust footwall chronostratigraphy is indicated by detrital zircon age spectrum differences from central western to far western arunachal nonetheless the late proterozoic rocks in the main central thrust hanging wall and footwall in far western arunachal can be correlated to each other and to previously analyzed rocks in the south tibet detachment hanging wall to the west and in the indian craton to the south these findings are synthesized in a reconstruction showing late triassic india lhasa rifting and cenozoic eastern himalayan construction via in situ thrusting of basement and cover sequences along the north indian margin

subsidence history of the tethys himalaya abstract this article reconstructs the evolution of the passive northern margin of peninsular india facing the neotethys from the earliest rifting stages in the carboniferous to final collision with the active southern margin of asia in the early eocene classical techniques of basin analysis were applied to an extensive and coherent stratigraphic data base facies analysis biostratigraphic dating and palaeoenvironmental interpretation of an over 10 km thick sedimentary succession from eight main composite sections allowed us to draw accurate sedimentation and backstripped subsidence curves and to place quantitative constraints on the palaeotectonic scenario inferred from the sedimentary record in each of the investigated composite sections three major stratigraphic gaps are consistently recognised in the rift sequence the rift unconformity mississippian the carboniferous permian hiatus largely kasimovian to asselian and the break up unconformity mid sakmarian two or even all three gaps may merge into a single hiatus spanning up to 70 ma overall gaps are associated with rift shoulder uplift which after calculation of backstripped subsidence sums up to 600 m at least in three of the investigated sections thermal subsidence and low sedimentation rates are documented by the mid permian to middle triassic drift sequence deposited while the neotethys was expanding between northern gondwana and the detached peri gondwanan blocks a marked increase in accumulation rates is recorded in the carnian norian but calculations of uniform lithospheric stretching suggest that extension was minor and associated with tectonic processes affecting distant parts of gondwana the tethys himalayan margin was uplifted around the jurassic cretaceous boundary at the onset of a major volcanic episode finally uplift exceeding in magnitude all previous events is documented by the uppermost units of the stratigraphic column deposited during the earliest stages of collision between india and asia in the latest paleocene to early eocene

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

provenance of late triassic sediments in central lhasa terrane tibet and its implication abstract in southern tibet late triassic sequences are especially important to understanding the assembly of the lhasa terrane prior to indo asian collision we report new data relevant to the provenance of a late triassic clastic sequence from the mailonggang formation in the central lhasa terrane tibet petrographic studies and detrital heavy mineral assemblages indicate a proximal orogenic provenance including volcanic sedimentary and some ultramafic and metamorphic rocks in situ detrital zircon hf and u pb isotope data are consistent with derivation of these rocks from nearby triassic magmatic rocks and basement that comprise part of the newly recognized late permian triassic sumdo cuoqen orogenic belt the new data suggests correlation with the upper triassic langjiexue group which lies on the opposing southern side of indus yarlung ophiolite sediments from both the mailonggang formation and langjiexue group are interpreted to represent formerly contiguous parts of a sequence deposited on the southern flanks of the sumdo cuoqen belt

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

calving processes at a grounded ice cliff repeat photographs and field survey reveal the mechanism of short term ice cliff evolution at maud glacier a temperate lake calving glacier in new zea land calving is cyclic each cycle involving four stages 1 waterline melting and collapse of the roof of a sub horizontal notch at the cliff foot 2 calving of ice flakes from the cliff face leading to a growing overhang from the waterline upwards and crack propagation from the glacier surface 3 large but infrequent calving of slabs in response to the devel oping overhang returning the cliff to an initial vertical profile 4 rare subaqueous cal ving of a submerged ice foot results indicate that the rate controlling process is the speed of waterline melting and that calving rate is independent of water depth at least at time scales of weeks to months slowly calving lake terminating glaciers have mass balances more negative than land terminating glaciers but nevertheless advance and retreat in response to mass balance driven changes in ice velocity

detrital zircon provenance of the late triassic songpan ganzi complex sedimentary record of collision of the north and south china blocks the majority of the songpan ganzi triassic flysch sequence is believed to have derived from denudation of the dabie and sulu ultrahigh pressure uhp metamorphic belt in eastern china e g nie et al 1994 1 zhou and graham 1996 2 however intense debate still exists on the sources of

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

the tethys himalayan passive margin from late triassic to early cretaceous south tibet the mesozoic succession of south tibet both in lithologies and stratigraphic thicknesses compares much more closely with that of central nepal than has been reported in the literature facies distribution from relatively proximal environments in the south to more distal settings in the north reflects the paleogeography of the tethys himalaya passive margin representing the southern edge of neotethys as in central nepal and nw himalaya accumulation rates increased greatly in the latest triassic when very thick shelfal siliciclastics and locally volcaniclastics tarap formation were followed by coastal sandstones zhamure formation contrary to reports in the literature this latter unit reaches well into the liassic at least in proximal southern sectors the base of the overlying kioto group yielding rich faunal associations characterized by benthic foraminifers and lithiotis similar to those of western tethys carbonate platforms is dated as middle liassic most probably late pliensbachian the monotonous growth of carbonate ramps during the middle liassic to early dogger was interrupted by two siliciclastic episodes related to major paleogeographic changes in the toarcian middle part of the kioto group and in the bajocian bathonian laptal formation an early callovian flooding event ferruginous oolite formation widespread all along the tethys himalaya was locally followed by deposition of a markedly lenticular pelagic unit previously reported only from the thakkhola graben dangar formation the overlying spiti shale is reduced to only 20 m in southern sectors where it is not younger than the oxfordian whereas in northern sectors the unit is several tens of m thick and mainly ascribed to the tithonian volcaniclastic deposition wolong formation reported herein for the first time probably began as early as the kimmeridgian early tithonian and lasted until aptian times when it was replaced by sedimentation of relatively deep water marlstones this magmatic episode related to tectonic extension associated with the detachment of india from gondwanaland took place earlier in south tibet and progressively later in central nepal and northern india as in nepal volcanic products changed with time from predominantly basaltic composition to intermediate and bimodal character the early cretaceous sedimentary evolution of south tibet matches that of offshore nw australia

revision of the cretaceous paleogene stratigraphic framework facies architecture and provenance of the xigaze forearc basin along the yarlung zangbo suture zone abstract new field investigation structural analysis review of biostratigraphy stratigraphic framework facies architecture provenance and flow direction of the cretaceous paleogene sedimentary strata in southern tibet resulted in reinterpretation of the evolution of the xigaze forearc basin xfb the xfb is comprised by flysch dominant xigaze group consisting of ngamring chongdoi and sangzugang formations and of the shallow marine cuojiangding group padana qubeiya quxia and gyalaze formations with their ages herein revised as the albian coniacian and the santonian ypresian respectively the deep sea flysch represented by the ngamring formation constitutes the early sedimentary fill of the xfb it was subdivided into five megasequences ms1 ms5 in order the early submarine fan facies stage channel submarine fan stage the mature submarine fan stage the highstand submarine fan stage and outer fan pelagic stage the paleocurrent flows were eastwards and westwards during the early and late stages of basin development and northwards and southwards during its middle stage indicating typical forearc basin sedimentation with longitudinal supply and lateral filling provenance studies point to multiple sources with andesitic debris sourced from the jurassic lower cretaceous yeba formation and sangri group formed in the volcanic island arc chains in the southern gangdese the four periods of the xfb development are 1 the formation of the xfb basement by the xigaze ophiolite and completed before the aptian the coeval deposits on the shelf are the sangzugang formation carbonate 2 the earliest xfb deposits of the earliest aptian age ca 125 120 ma represented by the chongdoi formation related to the residual forearc 3 composite forearc developed represented by the late albian late cenomanian flysch megasequences ms1 ms2 and the turonian coniacian flysch megasequences ms3 ms5 respectively and 4 the final stage of the xfb development started the terminal forearc stage represented by the late late cretaceous early paleogene shallow marine cuojiangding group and terminated during middle ypresian when the gyalaze formation was deposited

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

exhumation of the dabie shan ultra high pressure rocks and accumulation of the songpan ganzi flysch sequence central china the presence of coesite and diamond bearing ultra high pressure uhp metamorphic rocks in the dabie and sulu regions central china suggests that a 100 km thick crustal section 4 x 106 km6 in volume has been denuded this volume is comparable to that represented by the 10 15 km thick middle to upper triassic flysch rocks in the songpan ganzi region regional geology and radiometric dates are compatible with an interpretation that the majority of these sedimentary rocks were derived from denudation of the orogenic belt between north and south china blocks following their latest paleozoic to triassic collision this correlation implies a high denudation rate of 4 mm yr that may have been in part promoted by tropical precipitation and extreme topographic relief for as long as 25 m y

multiple sources of the upper triassic flysch in the eastern himalaya orogen tibet china implications to palaeogeography and palaeotectonic evolution abstract the upper triassic flysch langjiexue group tentatively named the shannan terrane of the eastern himalaya orogen has been tectonically assigned either to the tethys himalaya or the yarlung zangbo suture zone yzsz in this work geochronology of detrital zircon u pb isotope shows that the shannan terrane is characterized by the population of 260 200 ma peak ca 240 ma strongly supporting the view of no affinity to the tethys himalaya the detrital zircons dated as 400 290 ma display relatively positive ehf t values of 5 0 to 15 0 with t dm c ages of 2 6 1 3 ga for the shannan terrane whereas highly negative are of 20 0 to 5 0 for the lhasa terrane indicating that the two terranes have different devonian carboniferous sources numerous cr spinels found in the shannan terrane but not in the lhasa terrane exhibit contents in cr 2 o 3 and cr of mainly 44 100 and 48 95 in tio 2 of 0 01 1 0 and in al 2 o 3 of 5 257 respectively denoting several parent lithologies these differences suggested that the shannan terrane has multiple sources not only from the lhasa terrane but also from oceanic island arc seamount and mid ocean ridge areas as well as likely from greater india and australia considering the early cretaceous diabase dykes within the upper triassic flysch defined to the comei bunbury large igneous province we propose that the langjiexue group could have been deposited on the ocean between india and australia and would have not stopped till the lhasa terrane was separated from australia during the terminal triassic according to the cenozoic deformation and metamorphic history and palaeogeography of the langjiexue group we postulate that the shannan terrane could have been loaded onto the greater india during the middle early cretaceous and subsequently drifted northward to the collision zone of india and asia implying that it does not represent an accretionary prism within the yzsz

structural sequence and geochronology of the qomo ri accretionary complex central qiangtang tibet implications for the late triassic subduction of the paleo tethys ocean abstract the late paleozoic qomo ri accretionary complex qrac in the central qiangtang region of tibet lies at the southern margin of the longmu co shuanghu suture qrac is tectonically linked with the nierong and jitang metamorphic complexes in eastern tibet and the yunling and lancang complexes in western yunnan province sw china this metamorphic complex is mainly composed of late paleozoic passive continental marginal strata of the south qiangtang basin which was underthrust beneath north qiangtang in the late triassic at least three stages of deformation d1 d2 and d3 with two corresponding metamorphic events m1 and m2 were identified within the qrac d1 is characterized by a penetrative foliation s1 bearing a dextral shear and a corresponding m1 mineral assemblage of phengite garnet and quartz this deformation was interpreted to be the result of the northwestward oblique subduction of the paleo tethys ocean and dated at 211 219 ma by phengite 40ar 39ar ages d2 a subsequent compression deformation followed d1 immediately and exhibits flexural folds and pervasive axial crenulation in foliation s2 deformations from d1 to d2 indicate that an oblique oceanic subduction was immediately followed by a collision between the north and south qiangtang blocks along the longmu co shuanghu suture the d3 recorded by minor folds and divisional axial cleavage s3 is related to a giant arc structure with an extension of 50 km

tectonic evolution of the early mesozoic blueschist bearing qiangtang metamorphic belt central tibet this is the published version copyright 2003 american geophysical union all rights reserved

ultra long distance littoral transport of orange sand and provenance of the skeleton coast erg namibia abstract quantitative provenance analysis based on high resolution bulk petrography and heavy mineral data on beach and dune sands integrated with detrital zircon geochronology and chemical analyses of pyroxene garnet and staurolite demonstrates that sand derived from the orange river is carried by powerful and persistent longshore currents as far as northern namibia and southern angola 1750 km north of its mouth this is the longest cell of littoral sand transport documented so far compositional forward modeling indicates that 80 of dune sand in the skeleton coast is orange derived the remaining 20 being supplied by slow erosion of the damara orogen chiefly via the swakop river a decrease in basaltic rock fragments and pyroxene with relative enrichment in garnet staurolite tourmaline and other metamorphic minerals north of walvis bay indicates that only one third of beach sand in the 350 km dune free gap between the namib and skeleton coast ergs is orange derived the remaining two thirds being supplied largely by the swakop river draining the damara orogen although volcanic gravel becomes dominant in beaches of the skeleton coast north of the uniab mouth detritus from cretaceous etendeka lavas accounts for only 4 of beach sand reflecting limited sand generation in the arid catchment contributions from the kunene river to either dune or beach sands is ruled out indicating that gem diamonds found in placer deposits along the coast of namibia are all derived from the orange river

building the new england batholith eastern australia linking granite petrogenesis with geodynamic setting using hf isotopes in zircon abstract u pb and hf isotope analysis of zircons from granitoids of the permian triassic new england batholith eastern australia was carried out to provide constraints on the evolution of an isotopically and compositionally diverse batholith incipient plutonism in the early permian resulted in the formation of isotopically evolved peraluminous granodiorites of the hillgrove suite following this mixing between crustal derived 5 8 ehf units and depleted mantle derived magmas 13 18 ehf units was responsible for the formation of the c 282 ma bundarra suite the strongly metaluminous and isotopically depleted granites of the c 268 ma clarence river suite 11 16 ehf units signify an increased role of isotopically depleted magmas during the formation of plutonic rocks in the middle permian interestingly this isotopic and chemical transience coincides with orogenic extension that was associated with the relocation for the southern new england orogen neo from a continental margin accretionary setting to that of a back arc basin following attenuation the neo was thickened by contraction during the hunter bowen event 265 255 ma forming after the hunter bowen event the metaluminous rocks of the c 256 ma moonbi suite were the product of mixing between magmas derived from evolved metaigneous rocks and enriched mantle 3 8 ehf units we attribute the switch in isotopic character from highly depleted i e clarence river suite to evolved i e moonbi suite to crustal thickness before i e thin and after i e thick the hunter bowen event evidence of renewed mixing between depleted and evolved magmas characterises the formation of the c 249 ma uralla suite 7 16 ehf units which interestingly was coeval with renewed orogenic extension in the early triassic finally the melting of deep crustal basalts below the southern new england orogen in the middle triassic c 233 ma resulted in the formation of moderately depleted leucomonzogranites and a type magmas 9 12 ehf units through combining new u pb and hf zircon isotope data with pre existing whole rock nd and geochemical data a link between geodynamic setting and granite petrogenesis has been identified where i in thick orogens granites formed via partial melting of the crust and lack a significant depleted component ii in thin orogens granites form by mixing of crustal derived and depleted mantle derived magmas and iii in highly attenuated orogens granites can be extremely depleted and dominantly derived from the melting of upper mantle sources this relationship may be associated with the development or reactivation of lithosphere scale detachments during orogenic extension that could facilitate the transportation of depleted magmas into the crust

tertiary deformation history of southeastern and southwestern tibet during the indo asian collision geologic mapping and geochronological analysis in southwest kailas area and southeast zedong area tibet reveal two major episodes of tertiary crustal shortening along the classic indus tsangpo suture in the yalu river valley the older event occurred between ca 30 and 24 ma during movement along the north dipping gangdese thrust the development of this thrust caused extensive denudation of the gangdese batholith in its hanging wall and underthrusting of the xigaze forearc strata in its footwall examination of timing of major tectonic events in central asia suggests that the initiation of the gangdese thrust was approximately coeval with the late oligocene initiation and development of north south shortening in the eastern kunlun shan of northern tibet the nan shan at the northeastern end of the altyn tagh fault the western kunlun shan at the southwestern end of the altyn tagh fault and finally the tian shan north of the tarim basin such regionally synchronous initiation of crustal shortening in and around the plateau may have been related to changes in convergence rate and direction between the eurasian plate and the indian and pacific plates the younger thrusting event along the yalu river valley occurred between 19 and 10 ma along the south dipping great counter thrust system equivalent to the locally named renbu zedong thrust in southeastern tibet the backthrust system in south central tibet and the south kailas thrust in southwest tibet the coeval development of the great counter thrust and the north himalayan granite gneiss dome belt is consistent with their development being related to thermal weakening of the north himalayan and south tibetan crust due perhaps to thermal relaxation of an already thickened crust created by the early phase of collision between india and asia or frictional heating along major thrusts such as the main central thrust beneath the himalaya

provenance analysis of the mesozoic hoh xil songpan ganzi turbidites in northern tibet implications for the tectonic evolution of the eastern paleo tethys ocean 1 mesozoic strata of the hoh xil songpan ganzi complex in northern tibet are exposed in a vast 370 000 km2 triangle shaped orogenic belt bound by the longmen shan thrust belt in the east the kunlun terrane and north china block in the north and the qiangtang terrane and yidun arc in the south these strata consist of middle upper triassic submarine fan and deep marine facies rocks that were deposited in the paleo tethys ocean late triassic early jurassic contractional deformation in the eastern hoh xil songpan ganzi complex marks the demise of the paleo tethys ocean basin and the accretion of the gondwana derived qiangtang terrane to eurasia we conducted geological mapping regional stratigraphic analyses and u pb geochronology of detrital zircons n 4128 on the mesozoic sequences exposed in the hoh xil songpan ganzi complex kunlun terrane and qiangtang terrane we identify for the first time marine silciclastic sandstone and shale of jurassic age in the northwestern hoh xil songpan ganzi complex that unconformably overlie upper triassic turbidites zircon age data indicate that the middle upper triassic marine gravity flow deposits of the hoh xil songpan ganzi complex were shed from the north and south china blocks and middle late triassic ultrahigh pressure qinling dabie orogenic belt as well as the kunlun and qiangtang terranes in addition the detrital zircon results suggest vast sediment source to sink distances 1500 km for the middle upper triassic hoh xil songpan ganzi strata which is consistent with tectonic models for the paleo tethys ocean basin that incorporate significant components of horizontal tectonic transport like opening of large back arc basins in response to oceanic slab rollback

distributed deformation in southern and western tibet during and after the india asia collision field and radiometric data are used to describe and date strain and stress states in southern longitude 88 o to 91oe latitude 28 o to 30on and western tibet longitude 79 o to 82oe latitude 30 o to 34on we factorize deformation into syncollisional and postcollisional and we present stretching lineation and displacement orientation maps two sections across the indian shelf sequence and stress orientations calculated from mesoscale fault slip data in southern tibet syncollisional stretching and displacement directions trend 90 46 o and displacement is top to south synkinematic low grade metamorphism is dated at 50 ma at one locality in the indian shelf sequence underlying the main mantle thrust of the indus yarlung suture this implies paleocene onset of continental collision for the investigated section postcollisional structures comprise a backthrust group which includes foreland and hinterland directed thrusts reverse and strike slip faults and folds it dominates postcollisional deformation is concentrated along the indus yarlung suture and portrays n s compression otrend of 8o 17 o o2 of 97o 17o a strike slip group consists of conjugate strike slip faults is concentrated in east trending narrow highly deformed zones and indicates that n s compression is locally compensated by e w extension oof 15o 29 o o3 of 103o 30o synkinematic muscovite dates postcollisional deformation as late early miocene 17 5 ma at one locality at the suture strike slip and oblique normal 03 of 600 23 o oof 144o 21 o and normal o3 114o 16 o faulting dated between late miocene and recent and including active deformation represents dominant e w and minor n s extension due to e w stretching of southern tibet and oroclinal bending along the himalayan arc restoring syncollisional and postcollisional deformation yields a minimum of 67 258 km shortening across the indian shelf sequence incorporating recently published contraction estimates across the eastern himalaya yields minimum shortening between undeformed india and the indus yarlung suture of 66 536 km the himalaya tibet orogenic system south of the indus yarlung suture had an initial width of 811 km in the southern tibetan section in western tibet imbrication of an ophiolite sequence of the bangong nujiang suture is top to south stretching lineation trend of 15o 18o and o3 of active deformation trends ese faulting along the shiquanhe fault zone which transfers displacement from the northern part of the karakorum fault to a system of rifts in western central tibet indicates dextral strike slip alternating with sinistral oblique normal faulting and block rotations around vertical axes during a prolonged shearing history the indian shelf sequence south of mount kailas shows top to south imbrication stretching lineation trend of 52o 60o both indian shelf rocks and oligocene miocene kailas conglo merates record backthrusting and backfolding oof 33 o and recent e w extension 03 of 85o 28o

stratigraphy of the upper cretaceous and lower tertiary strata in the tethyan himalayas of tibet tingri area china the 1500 m thick marine strata of the tethys himalaya of the zhepure mountain tingri tibet comprise the upper albian to eocene and represent the sedimentary development of the passive northern continental margin of the indian plate investigations of foraminifera have led to a detailed biozonation which is compared with the west tethyan record five stratigraphic units can be distinguished the gamba group upper albian lower santonian represents the development from a basin and slope to an outer shelf environment in the following zhepure shanbei formation lower santonian middle maastrichtian outer shelf deposits continue pebbles in the top layers point to beginning redeposition on a continental slope intensified redeposition continues within the zhepure shanpo formation middle maastrichtian lower paleocene the series is capped by sandstones of the jidula formation danian deposited from a seaward prograding delta plain the overall succession of these units represents a sea level high at the cenomanian turonian boundary followed from the turonian to danian by an overall shallowing upward megasequence this is followed by a final transgression regression cycle during the paleocene and eocene documented in the zhepure shan formation upper danian lutetian and by upper eocene continental deposits the section represents the narrowing and closure of the tethys as a result of the convergence between northward drifting india and eurasia the plate collision started in the lower maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift stronger subsidence and deposition took place from the middle maastrichtian to the lower paleocene the final closure of remnant tethys in the tingri area took place in the lutetian

sedimentologic and stratigraphic constraints on the orientation of the late triassic northern indian passive continental margin abstract the orientation and distribution of the northern indian passive continental margin basin during different epochs constrained the geometric characteristics of the hyperextended northern indian edge greater india traditional paleogeographic reconstructions envisage the late triassic northern indian passive continental margin as e w trending whereas paleomagnetic data support an 55 counterclockwise rotation during northward drifting this case study of upper triassic units from the northern indian margin based on facies analysis sandstone petrography heavy mineral assemblages u pb detrital zircon geochronology and stratigraphic correlation from the zanskar range to southern tibet provides new constraints and suggests that the northern indian passive continental margin might have been n s trending in the late triassic given the dominance of quartz sandstones with zircon tourmaline and rutile indicating a provenance from continental blocks and the recycling of older quartz rich sandstones and detrital zircon age spectra characterized by a neoproterozoic detrital zircon u pb age peak 921 13 ma the upper triassic sandstones widespread along the tethyan himalayas may have been partly derived from the eastern ghats mobile belt in eastern india and the rayner orogen in eastern antarctica the upper triassic quartzite series comprises feldspatho quartzose to pure quartzose sandstones with intercalated bioclastic oosparites deposited in backshore foreshore and shoreface coastal environments without considering the subsequent counterclockwise rotation of india the consistent pattern of the upper triassic bidirectional e w paleocurrent observed throughout the himalaya suggests that the paleoshoreline was striking near n s approximately perpendicular to the regional orientation of the northern indian margin progressive eastward thickening of the sandstone layers and eastward younging of the quartzite series suggest diachronous sedimentation such stratal patterns and the strike of the late triassic paleoshoreline were attributed to the neo tethys transgression from the zanskar range to southern tibet

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

sandstone provenance and tectonic evolution of the xiukang melange from neotethyan subduction to india asia collision yarlung zangbo suture south tibet abstract the xiukang melange of the yarlung zangbo suture zone in south tibet documents low efficiency of accretion along the southern active margin of asia during cretaceous neotethyan subduction followed by final development during the early paleogene stages of the india asia collision here we present integrated petrologic u pb detrital zircon geochronology and hf isotope data on different types of sandstone blocks in the xiukang melange three groups of sandstone blocks with different provenance and depositional setting are distinguished by their petrographic geochronological and isotopic fingerprints blocks of turbiditic quartzarenite originally sourced from the indian continent were deposited in pre cretaceous time on the northernmost edge of the indian passive margin and eventually involved into the melange at the early stage of the india asia collision two distinct groups of volcaniclastic sandstone blocks were derived from the central lhasa block and gangdese magmatic arc one group was deposited in the trench and or on the trench slope of the asian margin during the early late cretaceous and the other group in a syn collisional basin just after the onset of the india asia collision in the early eocene the largely erosional character of the asian active margin in the late cretaceous is indicated by the scarcity of off scraped trench fill deposits and the relatively small subduction complex developed during limited episodes of accretion the xiukang melange was finally structured in the late paleocene eocene when sandstone blocks of both indian and asian origin were progressively incorporated tectonically in the suture zone of the nascent himalayan orogen

xigaze forearc basin revisited south tibet provenance changes and origin of the xigaze ophiolite our new stratigraphic sedimentological and micropaleontological analysis integrated with basalt geochemistry sandstone petrography and detrital zircon u pb and hf isotope data suggests the revision of current models for the geological evolution of the asian active margin during the cretaceous the xigaze forearc basin began to form in the late early cretaceous south of the gangdese arc during the initial subduction of the neotethyan oceanic lithosphere under the lhasa terrane well preserved stratigraphic successions document the classical upwardshallowing pattern of the forearc basin strata and elucidate the origin of the associated oceanic magmatic rocks the normal midocean ridge basalt n morb geochemical signature and stratigraphic contact with the overlying abyssal cherts chongdui formation indicate that the xigaze ophiolite formed by forearc spreading and represents the basement of the forearc sedimentary sequence volcaniclastic sedimentation began with thick turbiditic sandstones and interbedded shales in the late albian santonian ngamring formation followed by shelfal deltaic and fl uvial strata padana formation with fi nal fi lling of the basin by the campanian age forearc sandstones do not show the classical trend from feldspatholithic volcaniclastic to quartzo feldspathic plutoniclastic compositions indicating limited unroofi ng of the gangdese arc prior to collision u pb age spectra of detrital zircons are unimodal with a 107 ma peak in the lower ngamring formation 104 99 ma bimodal with a subordinate additional peak at 157 ma in the middle ngamring formation 99 88 ma and multimodal with more abundant pre mesozoic ages in the upper ngamring and padana formations 88 76 ma these three petrofacies with distinct provenances document the progressive erosional evolution of the gangdese arc with uplift of the central lhasa terrane and expanding river catchments to include the central lhasa terrane during the late cretaceous

zircon u pb geochronology and hf isotopic constraints on petrogenesis of the gangdese batholith southern tibet abstract during the mesozoic cenozoic northward neotethyan subduction and subsequent india asia collision gave rise to the extensive transhimalayan magmatism that stretches from burma and western yunnan through southern tibet to the ladakh and kohistan complexes to understand the age distribution and petrogenesis of the gangdese batholith the largest intrusive exposure along the transhimalayan magmatic belt fifty granitic samples were selected for in situ zircon u pb and hf isotopic analyses the u pb data suggest four discrete stages of magmatic activity i e 205 152 109 80 65 41 and 33 13 ma respectively with the 65 41 ma stage being the most prominent the hf isotopic data indicate that the gangdese batholith is overwhelmed by positive e hf t values which are comparable to those of the kohistan ladakh batholiths in the west but differ markedly from those of the chayu burma batholiths in the east most of the gangdese granites show similar and young hf model ages 1000 300 ma indicating their derivation from juvenile crust however those formed in the 65 41 ma stage exhibit more heterogeneous hf isotopic ratios with negative e hf t values being observed in some granites younger than 50 ma suggesting the involvement of old indian continental crust in their petrogenesis this age may thus mark the onset of the india asia collision the newly established zircon u pb age and hf isotope database of the gangdese batholith can be used as a powerful tracer or fingerprint when studying the source to sink relation of the sediments eroded from the southern tibetan plateau

cenozoic tectonic evolution of asia a preliminary synthesis abstract asia has been a major testing ground for various competing models of continental deformation due to its relatively well understood plate boundary conditions in the cenozoic exceptional exposure of active structures and strain distribution and widespread syn collisional igneous activity as a proxy for the thermal state of the mantle and crust two cenozoic orogens dominate the continent the himalayan tibetan orogen in the east induced by the india asia collision and the turkish iranian caucasus orogen in the west induced by the arabia asia collision the development of the two orogens was accomplished by shortening in the early stage followed by strike slip faulting and extension in the late stage in the himalayan tibetan orogen shortening across two discrete thrust belts at 55 30 ma in southern and northern tibet created a large intracontinental basin the paleo qaidam basin in between subsequent crustal thickening and a possible thermal event in the mantle e g convective removal of central tibetan mantle lithosphere may have raised the elevation of this early intra plateau basin up to 2 3 km to its current height collision between india and asia also caused lateral extrusion of southeast asia between 32 ma and 17 ma the latest stage of the india asia collision was expressed by north trending rifting and the development of trench facing v shaped conjugate strike slip faults in central mongolia central tibet eastern afghanistan and southeast asia in the turkish iranian caucasus orogen early crustal thickening in the orogenic interior began at or prior to 30 20 ma this style of deformation was replaced by strike slip faulting at 15 5 ma associated with further northward penetration of arabia into asia westward extrusion of the anatolia turkey block and rapid extension across the sea of crete and sea of aegean the late stage extension in both orogens was locally related to extensional core complex development the continental margin extension of east asia was developed in two stages initially in a widely distributed zone that has an east west width of 500 800 km during 65 35 ma which was followed by localized extension and opening of back arc basins associated with the development of spreading centers at 32 17 ma e g japan sea or east korea sea bohai bay and south china sea opening of the back arc basins could be induced by 1 rapid eastward migration of the western pacific trench system or 2 oblique subduction of pacific plate beneath asia that had produced a series of en echelon right slip primary shear zones linking with back arc spreading centers oriented obliquely to the strike of the nearby trench since 15 ma the eastern margin of asia became contractional in the east west direction as indicated by the collapse of back arc basins in the western pacific and the development of fold thrust belts along the eastern continental margin coeval with the contraction is widespread east west extension in siberia north china and the tibetan plateau the above observations can be explained by a change in boundary condition along the eastern margin of asia that allowed the thickened asian continent to spread eastward causing east west extension in its trailing edge and east west compression in its leading edge in west asia continental margin extension started at about 25 20 ma in the aegean and cretan regions which was associated with a rapid southward retreat of the hellenic arc the complex evolution of cenozoic deformation in asia may be explained by a combined effect of temporal changes in plate boundary conditions thermal evolution of the upper mantle perturbed by collisional tectonics and the built up of gravitational energy through crustal thickening and thermal heating although the past research in asia has treated the india asia and arabia asia convergence as separate collisional processes their interaction may have controlled the far field cenozoic deformation in asia the most pronounced result of this interaction is the creation of a northeast trending 300 400 km wide and 1500 km long zone of northwest striking right slip faults which extends from the zagros thrust belt in the south to western mongolia in the north and links with the active tian shan and altai shan intracontinental orogens cenozoic deformation and coeval igneous activity spatially overlap with one another in the himalayan tibetan and turkish iranian caucasus orogens a large cenozoic magmatic gap exists between tibet in the south and mongolia in the north where cenozoic deformation has not been associated with any coeval igneous activity finally cenozoic igneous activity is always associated with jurassic cretaceous magmatic arcs suggesting a causal relationship between the early arc magmatism and later syn collisional magmatism

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

evidence for early 44 ma himalayan crustal thickening tethyan himalaya southeastern tibet abstract comprehensive understanding of himalayan orogenesis is limited in part by a poor knowledge of the eohimalayan episode a phase of tectonic activity predating the better understood neohimalayan crustal thickening associated with coaxial deformation along the main central thrust the cambo ordovician to tertiary metasedimentary sequences outcropping within the tethyan himalaya are the structurally highest units of the himalayan fold and thrust belt they and are inferred to have been the first to have accreted to asia a compilation of data from transects along the length of the main himalayan arc shows that the tethyan sequences have experienced at least five deformation events although the timing of these episodes is poorly constrained emplacement of a series of undeformed granitoid bodies following the second of these events which accounts for the majority of crustal thickening in the tethyan himalayan units is constrained by u pb zircon dating to be older than 44 1 1 2 ma thus significant crustal thickening had occurred along the length of the proto himalayan arc by the mid eocene or within 10 to 20 myr of the initiation of himalayan orogenesis

uncoupled o and hf isotopic systems in zircon from the contrasting granite suites of the new england orogen eastern australia implications for studies of phanerozoic magma genesis abstract the permo triassic granites of the new england orogen eastern australia were emplaced into a volcanic arc complex accreted to the eastern gondwana margin in the late devonian or early carboniferous zircon u pb dating shows that the s type hillgrove 297 ma and bundarra 287 ma supersuites predated intrusion of the i type moonbi supersuite 250 ma by up to 50 ma the high 18ozrn of the s type granites 10 0 11 5 and range of u pb ages 370 300 ma and 18ozrn 5 10 of their inherited zircon cores show that their source rocks were predominantly weathered carboniferous volcaniclastics the youngest deposited

convection in the atmospheric boundary layer abstract recent advances in the study of clear and partly cloudy convective boundary layers are reviewed the techniques and results of observational studies of the structure and dynamics of convective elements are discussed these findings have important consequences for pollution dispersion they also form the basis for a test of les dispersion models which is more discriminating than those based on replication of observed turbulence statistics several new approaches to cbl similarity theory and parameterization have appeared they avoid some of the problems associated with the over simplification of previous techniques particularly noteworthy is the ability to handle counter gradient fluxes with relatively simple models progress towards parameterization of cbl turbulence in the presence of horizontal inhomogeneity of the atmosphere or surface has been slower efforts to locate the limits of validity of the assumption of horizontal homogeneity have been more successful than the efforts to develop parameterizations which do not rely upon it mesoscale models need cbl parameterizations which are valid over complex terrain and in the presence of strong differential advection and mean vertical motion les models may prove useful in producing the data sets on which such parameterizations could be based

deposystem architectures and lithofacies of a submarine fan dominated deep sea succession in an orogen a case study from the upper triassic langjiexue group of southern tibet abstract over thirty stratigraphic sections of the himalaya orogen upper triassic langjiexue group in southern tibet china were studied to interpret the environments and lithofacies the facies associations channel a lobe b levee interchannel c and basin plain d with nine facies a1 3 b1 3 and c1 3 were distinguished they form six architectural elements channel interchannel overbank levee crevasse splay outer fan lobe fan fringe and basin plain taking into account the facies analysis sub deposystem correlation paleocurrent dispersal pattern and restoration of primary stratal width the langjiexue group displays the architecture of a coalescing submarine fan dominated deep sea deposystem measuring about 400 500 km 600 700 km in size or even more one of the largest pre cenozoic submarine fans ever reported subdivisionally four fans lacking inner fans could have coalesced laterally within the submarine fan deposystem and at least six submarine fan developments were vertically succeeded by mid to outer fan deposits with progradational to retrogradational successions according to the range of 30 70 of sandstone content the fan deposystem is mud and sand rich suggesting a medium far over 400 600 km transport of sediment from the source area

orogenesis without collision stabilizing the terra australis accretionary orogen eastern australia the neoproterozoic to end paleozoic terra australis orogen extended along the gondwana margin of the paleo pacific ocean and it now provides a detailed record of orogenic activity and continental stabilization within an ongoing convergent accretionary plate margin new geochronological data from end paleozoic plutonic and volcanic rocks associated with the gondwanide orogeny in the new england region of eastern australia integrated with information on the nature and timing of associated sedimentation deformation and metamorphism allow resolution of a high fidelity record of orogenesis at the end of the carboniferous around 305 ma convergent margin magmatism which had been active along the western margin of the new england region terminated and was followed by a short pulse of regional compressional deformation and metamorphism marking the commencement of the tablelands phase of gondwanide orogenesis deformation was almost immediately followed by the onset of clastic sedimentation and local calc alkaline volcanism dated at 293 ma in the extensional barnard basin emplacement of the two new england s type granitic suites the bundarra and the hillgrove suites along with localized high temperature low pressure metamorphism was essentially contemporaneous ranging in age from 296 to 288 ma and overlapped in time with i type magmatism and the switch from regional compression to extension and barnard basin rifting the hunter bowen phase of the gondwanide orogeny commenced with contractional deformation resulting in termination of sedimentation in the barnard basin and regional deformation and metamorphism across new england and into the sydney and gunnedah basins to the west at around 265 260 ma contractional loading of the sydney and gunnedah basins resulted in their conversion from extensional to foreland basins which received ongoing pulses of sediment from the new england orogenic welt until 230 ma the hunter bowen phase was associated with widespread i type plutonism and volcanic activity in new england that ceased around 230 ma marking the termination of gondwanide orogenesis orogenesis occurred in an evolving convergent plate margin setting s and i type magmatic activity ranging in age from ca 300 to 230 ma represents a stepping out of arc magmatism from the western margin of new england prior to 305 ma into the preexisting arc trench gap there is no evidence that deformation was related to the collision of the convergent margin with a major lithospheric mass and the widespread development of extensional basins in the eastern third of australia in the early permian indicates control by phenomena acting on a continental scale probably changing plate kinematics associated with the amalgamation of pangea

upper triassic turbidites of the northern tethyan himalaya langjiexue group the terminal of a sediment routing system sourced in the gondwanide orogen abstract the upper triassic langjiexue group exposed south of the yarlung zangbo suture zone in south tibet shows sedimentary features different from typical tethyan himalayan successions and its origin is controversial in this article we combine field observations with paleocurrent petrologic geochronological and isotopic data to determine the provenance of langjiexue sandstones these middle to distal deep sea fan turbidites are crosscut by lower cretaceous diabase sills and dikes generated during rifting of india from gondwana indicating that the langjiexue group was originally deposited along or adjacent to the northern passive continental margin of india flute casts at the base of turbidite beds indicate mostly wnw ward paleocurrents pointing to provenance from a source located east of the depositional area common volcanic fragments and plagioclase grains together with a cluster of 400 200 ma aged magmatic zircons with uniform e hf t values from 5 to 10 are incompatible with any nearby sources including the qiantang block the lhasa block or the india subcontinent and indicate instead supply from a long lived magmatic arc terrane considering what is known about late triassic paleogeography a plausible source for langjiexue sediments is represented by the gondwanide orogen generated during subduction of the pan pacific oceanic lithosphere beneath southeastern gondwana this scenario is supported by the age range and hf isotopic signatures of late paleozoic early mesozoic zircons contained in langjiexue turbidites as in coeval turbidites exposed in western myanmar new data are needed to confirm falsify the existence of a thousand km long sediment routing system similar to the modern amazon which sourced in a cordillera type orogen rising along the southeastern margin of gondwana crossed an entire continent to feed turbiditic fans now exposed from western myanmar to the northern tethys himalaya

reconstruction of eastern gondwanaland substantial additions of large continental blocks to the smith et al 1 model of eastern gondwanaland are proposed here largely on the basis of the distribution of key land floras tropical and subtropical marine faunas lithofacies patterns and the identification of a triassic magmatic arc that characterized all the eastern margin of gondwanaland the continental fragments that must have been rifted from northern australia new guinea in the jurassic are identified as south tibet burma thailand malaya and sumatra the original site of deposition of the subtropical permian limestones and tropical late triassic limestones overthrust onto the northern margin of australia by the late cenozoic collision2 is located in this greater gondwanaland palaeomagnetic data except those from malaya3 support this reconstruction

late triassic paleogeographic reconstruction along the neo tethyan ocean margins southern tibet abstract sandstone petrographic and u pb detrital zircon analyses of upper triassic sedimentary rocks from the northern margin of india tethyan himalaya sequence and southern margin of eurasia lhasa terrane provide new constraints on the mesozoic paleogeography of neo tethyan ocean basins the upper triassic nieru formation of the tethyan himalaya sequence ths near lazi city 29 n 87 5 e is dominated by indian affinity precambrian detrital zircons which are typical of the majority of the ths however the upper triassic langjiexue formation of the ths exposed to the east at 90 93 e longitude includes significant populations of permian to early jurassic 291 184 ma detrital zircons for which there is no known indian source in addition the upper triassic nieru formation near kangma town 28 5 n 90 e located 200 km to the southeast of lazi city yielded detrital zircon age spectra that are similar to those of langjiexue formation based on detrital zircon age spectra comparisons we propose that both the langjiexue and nieru formations were derived from continental crustal fragments that were adjacent to the northwestern margin of australia furthermore we suggest that these ths units and age equivalent strata in northwest australia west sulawesi timor and west papua comprised a late triassic submarine fan along the northern australian shelf the upper triassic mailonggang formation in the southern lhasa terrane 35 km northeast of lhasa city 30 n 91 5 e is dominated by permian detrital zircons which were likely derived from proximal lhasa terrane sources the mailonggang formation differs from all age equivalent strata in the tethyan himalaya therefore we interpret that it was separated from greater india by the neo tethyan ocean

observation of playa salts as nuclei in orographic wave clouds during the ice in clouds experiment layer clouds ice l dry lakebed or playa salts from the great basin region of the united states were observed as cloud nuclei in orographic wave clouds over wyoming using a counterflow virtual impactor in series with a single particle mass spectrometer sodium potassium magnesium calcium chloride salts were identified as residues of cloud droplets importantly these salts produced similar mass spectral signatures to playa salts with elevated cloud condensation nuclei ccn efficiencies close to sea salt using a suite of chemical characterization instrumentation the playa salts were observed to be internally mixed with oxidized organics presumably produced by cloud processing as well as carbonate these salt particles were enriched as residues of large droplets 19 m compared to smaller droplets 7 m in addition a small fraction of silicate containing playa salts were hypothesized to be important in the observed heterogeneous ice nucleation processes while the high ccn activity of sea salt has been demonstrated to play an important role in cloud formation in marine environments this study provides direct evidence of the importance of playa salts in cloud formation in continental north america has not been shown previously studies are needed to model and quantify the impact of playas on climate globally particularly because of the abundance of playas and expected increases in the frequency and intensity of dust storms in the future due to climate and land use changes

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

isotopic evidence for rapid continental growth in an extensional accretionary orogen the tasmanides eastern australia the trace element signature of earth s continental crust resembles that of arc lavas but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra subduction zone magmatism we explore the role of coupled arc back arc accretionary processes in crust generation by considering the tectonic context of whole rock nd isotope and zircon hf o isotope data from igneous rocks of the australian tasmanides 515 230 ma which is thought to have evolved by the repeated opening and closure of sediment filled back arc basins behind a long lived subduction zone the significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective granitic rocks in this area define striking secular end ehf 18o trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity these trends reveal that juvenile magmatic input was enhanced during extensional back arc rifting episodes that immediately followed crustal thickening suggesting a relationship between slab rollback and continental growth interaction between juvenile magma and sedimentary units deposited during a preceding back arc rifting cycle was integral to the formation of stable continental material this highlights the importance of back arc environments for both the generation and differentiation of continental crust the juvenile component within the tasmanide igneous rocks increased from the cambrian to the triassic consistent with a diminished input from cratonderived metasedimentary material as the subduction zone migrated outboard of the gondwana margin subduction zone retreat formed large tracts of new crust in eastern australia at comparable rates to crust generation at modern island arcs providing a mechanism for rapid continental growth at convergent margins using isotopic tracers to link tectonic evolution and crust generation in modern and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation