accelerated extension of tibet linked to the northward underthrusting of indian crust the tibetan plateau is extending numerical simulations suggest that regional scale extension is caused by gravitational collapse of the plateau whereas rapid extension in the south is caused by underthrusting of the indian slab

introduction to the future of sequence stratigraphy evolution or revolution sequence stratigraphy was first developed as concepts and methods from the late 19th to mid 20th century by geologists such as barrell and sloss it is now at the forefront of how sedimentary geologists observe record model and predict strata the geological society william smith meeting in burlington house in september 2014 considered the current state and future developments in sequence stratigraphy and focused particularly on how the subject should progress either by evolution or by revolution we feel that this is a relevant question because of continuing debate and in some cases controversy about what sequence stratigraphy is how we do it and what it can be used for for example one of the major hindrances to progress has been the interweaving of description and interpretation mixing method with model this has been pointed out and discussed by various researchers helland hansen gjelberg 1994 burgess prince in press this thematic set of papers presents a sample of the state of the art in sequence stratigraphy representing how the method and model is now being debated and developed from a plea to retain the earliest version of the concept to the inclusion of more radical ideas stimulated from experimental stratigraphy the 2014 william smith meeting was generously funded by bg group eni neftex sepm and the geological society of london we would also like to thank all the geological society staff who hosted and facilitated the meeting

geochronology petrogenesis and tectonic significance of the jitang granitic pluton in eastern tibet sw china abstract the jitang granitic pluton which is situated in the southern margin of the north qiangtang block in eastern tibet may provide critical information about the source and derivation of the north qiangtang block during gondwana breakup and dispersion in this paper we report relevant data such as zircon u pb age whole rock major and trace element abundances and sr nd isotopes for the jitang pluton the major rock types of the pluton are granodiorite and biotite granite whole rock major element data reveal that the jitang pluton is a peraluminous s type granitic pluton the u pb age of zircons from the pluton is 219 1 1 7 ma which is 10 ma younger than the age of high pressure metamorphism in the longmu co shuanghu collisional suture between the north and south qiangtang blocks the jitang granitoids show pronounced negative ba eu sr anomalies high initial 87sr 86sr ratios from 0 7266 to 0 7389 and low end t values for from 11 1 to 13 2 which are remarkably similar to the gneisses and meta sedimentary rocks from the indian craton as well as the north qiangtang block the results from this study indicate that the jitang granitoids formed by melts derived from a crustal source with sr nd isotopic compositions similar to those of the indian cratonic crust we concur with the previous interpretation based on detrital zircon records that the north qiangtang block was derived from the indian gondwana

late triassic paleolatitude of the qiangtang block implications for the closure of the paleo tethys ocean abstract to better constrain the late triassic paleolatitude of the qiangtang block and the closure of the paleo tethys ocean a combined paleomagnetic and zircon u pb geochronological study has been conducted on the upper triassic jiapila formation volcanic rocks on the northern edge of the qiangtang block of central tibet 34 1 n 92 4 e these rocks are dated to 204 213 ma progressive thermal or alternating field demagnetization successfully isolated stable characteristic remanent magnetizations chrm that pass both the fold and reversal tests consistent with a primary magnetization these are the first volcanic based paleomagnetic results from pre cretaceous rocks of the qiangtang block that appear to average secular variation well enough to yield a reliable paleolatitude estimate based on our new paleomagnetic data from upper triassic lavas we conclude that the late triassic pole of the qiangtang block was located at 64 0 n 174 7 e with a 95 6 6 n 29 we compile published paleomagnetic data from the qiangtang block to calculate a late triassic latitude for the qiangtang block at 31 7 3 0 n the central paleo tethys ocean basin was located between the north china ncb and tarim blocks to the north and the qiangtang block to the south during late paleozoic early mesozoic a comparison of published early triassic paleopole from the qiangtang block with the coeval paleopoles from the ncb and tarim indicates that the paleo tethys ocean could not have closed during the early triassic and that its width was approximately 32 38 latitude 3500 4200 km however the comparison of our new combined late triassic paleomagnetic result with the late triassic poles of the ncb and tarim as well as numerous geological observations indicates that the closure of the paleo tethys ocean at the longitude of the qiangtang block most likely occurred during the late triassic

on shelf lower miocene oakville sediment dispersal patterns within a three dimensional sequence stratigraphic architectural framework and implications for deep water reservoirs in the central coastal area of texas through integrating three dimensional seismic and wireline log pattern data we found that the sequence stratigraphic architecture of the lower miocene oakville formation along the central part of the texas gulf coast reveals four third order sequences the lower two containing lowstand lst transgressive tst and highstand systems tracts hst and the upper two appearing to contain only tst and hst these sequences average 1 2 m y in duration the lowstand incised valley fill sandstones are massive as thick as 420 ft 73 m on wireline logs seismic stratal slices demonstrate that the incised valleys are dip oriented and more than 20 mi 32 km wide strata reflections within the incised valleys onlap the sides of the valley the third order tst comprise backstepping high frequency sequences seismic stratal slices and wireline log patterns within the tst suggest deltaic sediment dispersal patterns that appear reworked third order hst comprise aggradational to progradational high frequency sequences and seismic stratal slices and wireline log patterns indicate a variety of depositional environments that we interpreted as deltaic shoreface coastal plain and interdistributary the hst is significantly truncated by the overlying sequence boundary sandstone rich incised valley fills suggest that large amounts of sediment may have been transported through these channels and may have supplied lowstand deposits and associated reservoirs seaward of the previous shelf edge

indepth iii seismic data from surface observations to deep crustal processes in tibet 1 during the summer of 1998 active source seismic data were collected along a transect running 400 km nnw sse across the central tibetan plateau as the third phase of project indepth international deep profiling of tibet and the himalaya the transect extends northward from the central lhasa block across the jurassic bangong nujiang suture bns at 89 5 e to the central qiangtang block a seismic velocity model for the transect to 25 km depth produced by inversion of p wave first arrivals on 3000 traces shows 1 a 50 km wide region of low velocity at least 5 less than surrounding velocities extending to the base of the model at the bns 2 sedimentary cover for the southern qiangtang block that is 3 5 km thick 3 a distinct interface between sedimentary cover and qiangtang basement or underplated jurassic melange in the central qiangtang block and 4 evidence that the bangoin granite extends to a depth of at least 15 km the bns has little geophysical signature and appears unrelated to the 5 km northward shallowing of the moho which is associated with the bns in central tibet geophysical data along the main indepth iii transect show little evidence for widespread crustal fluids in contrast to the seismic bright spots found in southern tibet and to magnetotelluric evidence of fluid accumulations in eastern tibet a comparison between the global average and tibetan velocity depth functions offers constraints for models of plateau uplift and crustal thickening taken together with the weak geophysical signature of the bns these velocity depth functions suggest that convergence has been accommodated largely through pure shear thickening accompanied by removal of lower crustal material by lateral escape likely via ductile flow although we cannot resolve the details we believe lateral lower crustal flow has overprinted or destroyed evidence in the deep crust for the earlier assembly of tibet as a series of accreted terranes

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace element discriminant diagrams when dealing with ancient subalkaline volcanic rocks the alkali total iron magnesium afm diagram is of limited use in assigning a tholeiitic versus calc alkaline affinity because these eleme

cambrian to triassic geodynamic evolution of central qiangtang tibet abstract central qiangtang is a tectonic melange between the northern qiangtang terrane nqt and the southern qiangtang terrane sqt and it preserves a complete cambrian to triassic geological record related to tethyan evolution e g high pressure metamorphic rocks and ophiolites thus this region is the key to understanding the geodynamic processes that occurred during the dispersion of gondwana and the accretion of laurussia given previous studies on sedimentary paleomagnetic and seismic records this paper presents an integrated interpretation of ophiolites magmatism metamorphism and tectonism and reconstructs the cambrian triassic tectonic evolution of central qiangtang as described below 1 following the neoproterozoic early cambrian pan african orogeny and associated postcollisional extension the southward subduction of the proto tethys oceanic plate produced andean type magmatism along the northern margin of gondwana a back arc basin between the nqt and sqt further opened during the late cambrian early ordovician accompanying with trench retreat and overriding plate extension resulting from slab rollback 2 with the middle ordovician late silurian successive incorporation of micro continental terranes e g qaidam kunlun and tarim terranes into the northern margin of gondwana the back arc basin closed through subduction polarity reversal from southward to northward 3 during the late devonian early carboniferous the southward subduction of an oceanic plate to the north of the nqt separated the nqt and sqt through back arc extension consequently the nqt drifted northward rapidly and the back arc basin gradually evolved into a mature ocean basin i e longmu co shuanghu paleo tethys ocean lspto 4 subsequently a late carboniferous early permian continent continent collision between the nqt and the south china block scb resulted in the northward subduction of the lspto and the ongoing subduction probably induced the opening of a back arc basin between the nqt and the scb during the late permian 5 finally diachronous collision between the nqt and sqt closed the lspto during the early middle triassic and the termination of the collisional orogenic event was evidenced by strong late triassic magmatism related to postcollisional extension in the qiangtang block in this paper we propose that the opening and closure of back arc basins controlled the cambrian triassic tectonic evolution of central qiangtang which provides significant insights into the dispersion of gondwana and the accretion of laurussia

detection of the deep crustal structure of the qiangtang terrane using magnetotelluric imaging abstract to determine the deep electrical structure of the qiangtang terrane northern tibetan plateau we reanalysed three broadband magnetotelluric mt profiles collected by china university of geosciences wuhan in 1993 1994 and derived corresponding 2 d resistivity models in these models a remarkable high conductivity layer that was divided into northern and southern parts and that had formed an antiformal zone of high conductivity beneath the central qiangtang terrane was visible this high conductivity layer corresponds well with the trace of the southward subduction of the melange from the jinsha river suture inferred from surface geology according to our resistivity models the crust of the northern qiangtang terrane is mostly composed of melange the underplated melange may be closely related to the formation of the high conductivity layer and provide a reasonable explanation for the cause of special geophysical features in this area in addition the similarity between these resistivity models provides evidence that the qiangtang anticlinorium extends eastward to at least 92 e whereas the differences between them may offer an explanation for the gradual narrowing of the metamorphic belt from west to east in the central qiangtang terrane

strike variability of clastic depositional systems does it matter for sequence stratigraphic analysis current sequence stratigraphic models are two dimensional in nature and predict variability in depositional dip sections strike and dip variability of sediment supply to clastic depositional systems causes significant changes to sequence architecture so that contrasting yet coeval stacking patterns result these changes ultimately affect prediction potential based on fixed systems tract stacking patterns and relation to relative sea level curves identification of key surfaces in sequences rather than stacking patterns is the most reliable indicator of relative sea level history

practical problems in the application of the sequence stratigraphic method and key surfaces integrating observations from ancient fluvial deltaic wedges with quaternary and modelling studies sequence stratigraphy solved the basic problem that genetically related but different lithofacies were routinely assigned to different lithostratigraphic units defined by arbitrary vertical and horizontal cutoffs stratigraphically important stratal relationships and especially stratal terminations for example lapout can be observed in seismic data and can be documented in continuous outcrops such as in the deserts of the western interior of north america and in closely spaced well log data sets in sparse data sets interpolation of lapout patterns introduces uncertainty in correlation and designation of sequences and systems tracts and their associated surfaces diachroneity of fluvial terrace deposits is documented using detailed facies architectural studies and calls into question the assumed chronostratigraphic significance of many so called sequence boundaries identified in the rocks of the cretaceous interior seaway of north america sequence boundaries formed during prolonged sea level falls may be less chronostratigraphically significant than transgressive surfaces formed during rapid rises as a consequence flooding surfaces are theoretically more significant and also have greater utility as allostratigraphic boundaries although they may also exhibit diachroneity tectonic unconformities produce differential lithospheric deformation which results in angular unconformities although the angle of discordance may be very small in the cretaceous interior seaway of north america such unconformities may be expressed by marine erosion in distal basin settings regional isochronous bentonites provide useful marker beds that clearly illustrate angular discordance in the fluvial realm such tectonic discontinuities may be indicated by changes in palaeocurrent orientations as well as by provenance changes although sequence stratigraphy provides a powerful methodology and theoretical framework for correlating and understanding the evolution of stratigraphic successions in the context of changing accommodation allostratigraphy remains the only accepted scheme for the formal naming of stratigraphic units based on bounding discontinuities whatever type of sequence stratigraphy or allostratigraphy is preferred in all cases it is key to recognize that sequence stratigraphy at its heart is the re ordering correlation and sometimes renaming of stratigraphic units on the basis of bounding discontinuities and their correlative surfaces as opposed to the arbitrary lithofacies oriented approach using broad facies zones for example shazam lines or arbitrary cutoffs such as is used in traditional lithostratigraphy

contributions to sequence stratigraphy from analogue and numerical experiments the sequence stratigraphic model although no longer focused on eustasy and accommodation has been until recently based largely on observation and interpretation of outcrop and subsurface data this approach may be restrictive if the current model places limits on what is observed and how observations are interpreted to make progress in our understanding of strata the sequence stratigraphic model and method should be tested against and fully incorporate theoretical and experimental results that provide new knowledge of 1 autogenesis 2 intrinsic stratigraphic responses 3 alluvial grade and 4 scales appropriate to single depositional systems evolving with relative sea level changes more extensive inclusion of analogue and numerical experimental results could lead to significant modification and refinement of existing sequence stratigraphic models

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

how much systems tract scale three dimensional stratigraphic variability is present in sequence stratigraphy an answer from the middle miocene pearl river mouth basin prior sequence stratigraphic methods mainly employed two dimensional 2 d stacking patterns to reconstruct stratigraphic frameworks the future of sequence stratigraphy will pay more attention to systems tracts scale and three dimensional 3 d stratigraphic variability using 1 2 104 km2 4 63 103 mi2 3 d seismic data tied to regional 2 d seismic lines and 21 boreholes the present study examines systems tract scale and 3 d stratigraphic variability of the 14 8 13 8 ma pearl river shelf margin to deep water sedimentary prisms the studied prisms were divided into four main systems tracts namely highstand systems tract hst falling stage systems tract fsst lowstand systems tract lst and transgressive systems tract tst each systems tract is represented by a given clinoformal architecture and stacking pattern 1 clinothem sets with aggradation to progradation are hst 2 clinothem sets with progradation to degradation pd are fsst 3 clinothem sets with progradation to aggradation pa are lst and 4 clinothem sets with retrogradation are tst lst or hst in addition pearl river fsst and lst display downdip stratigraphic variabilities which are regionally manifested in at least three ways 1 shelf edge deltas linked downdip to basin floor fans 2 shelf edge deltas linked downdip without fans and 3 basin floor fans linked updip that lack deltas in along strike orientation the pearl river fsst could exhibit low angle progradation not just pd stacking the lst could present retrogradational stacking not just pa stacking therefore the physical position of a systems tract is reemphasized in terms of assigning a given systems tract the concepts of three systems tracts are then revised for chronostratigraphic significance the lst is the lowermost systems tract of a sequence presenting a normal regression of the shoreline as its diagnostic characteristic and including contemporaneous stratigraphic units laterally the hst is the upper systems tract of a sequence providing a normal regression of the shoreline as its diagnostic characteristic and including contemporaneous stratigraphic units laterally the tst is the middle systems tract of a sequence generating a backstep of the shoreline and excluding contemporaneous onlapping units of both the lst and hst laterally the fsst has not been revised because fsst may be a supply independent feature

triassic continental subduction in central tibet and mediterranean style closure of the paleo tethys ocean the qiangtang metamorphic belt qmb in central tibet is one of the largest and most recently documented high pressure hp to near ultrahigh pressure near uhp belts on earth lu hf ages of eclogite and blueschist facies rocks within the qmb are 244 223 ma indistinguishable from the age of uhp metamorphism in the qinling dabie orogen results of a u pb detrital zircon study suggest that protoliths of the qmb include upper paleozoic qiangtang continental margin strata and sandstones that were derived from a paleozoic arc terrane that developed within the paleo tethys ocean to the north we attribute qmb hp metamorphism to continental collision between the qiangtang terrane and a paleo tethys arc terrane this collision and the coeval south china north china collision may have slowed convergence between laurasia and gondwana derived terranes and initiated mediterranean style rollback and backarc basin development within much of the remnant paleo tethys ocean realm

carboniferous arc magmatism in the qiangtang area northern tibet zircon u pb ages geochemical and lu hf isotopic characteristics and tectonic implications abstract the longmu co shuanghu suture zone lssz which lies between the southern qiangtang baoshan block and northern qiangtang qamdo block on the tibetan plateau represents remnants of the paleo tethys ocean previous investigations have focused on the ophiolite high pressure zone and metamorphic belt in this zone whereas few studies have considered the arc magmatism the present study examines a suite of carboniferous arc magmatic rocks in the western region of the lssz that consist of acidic to basic volcanic rocks including rhyolite dacite andesite basaltic andesite basalt and pyroclastics zircon u pb dating of three samples two andesites and one dacite by laser ablation inductively coupled plasma mass spectrometry demonstrates that these rocks were emplaced at ca 351 346 ma the basalts have low cr and ni abundances indicating that they were generated by varying degrees of partial melting of an enriched lithospheric mantle that was metasomatized by subduction derived components zircons in the felsic rocks have positive e hf t values of 0 8 14 8 indicating an origin by varying degrees of partial melting of juvenile basaltic lower crust consisting mainly of underplated magmas with similar compositions to the basalts geochemical data show that the volcanic rocks are enriched in light rare earth elements and large ion lithophile elements e g th u and pb but are strongly depleted in high field strength elements e g nb ta and ti have high al 2 o 3 and low zr concentrations and are calc alkaline these magmas are therefore subduction related volcanic arc rocks indicating that paleo tethys subduction began in the early carboniferous

cenozoic tectonic subsidence in deepwater sags in the pearl river mouth basin northern south china sea the cenozoic tectonic subsidence of the deepwater area in the pearl river mouth basin northern south china sea is studied by subsidence analysis via backstripping calculations based on data of newly interpreted sequence boundaries in the subsidence analysis local porosity depth parameters were estimated based on well data the paleo water depth parameters and lithology were estimated for all grid nodes based on well data and sedimentary system maps and ages of sequence boundaries were adjusted according to the international chronostratigraphic chart v2013 01 sensitivity analysis shows that these are essential to ensure the quality of the subsidence analysis in the slope areas maps of tectonic subsidence rates of 18 cenozoic sequences were constructed and spatial temporal variations of the tectonic subsidence were discussed the subsidence was restricted in the baiyun and liwan sags before 30 ma and extended to uplifts after 30 ma this indicates that the 30 ma unconformity is the breakup unconformity that separated the syn rift and post rift sequences four substages of post rift subsidence were identified by cyclic changes in the rate and pattern of tectonic subsidence at boundaries of 23 3 ma 17 2 ma and 11 9 ma respectively anomalous post rifting tectonic subsidence was significant and totaled to similar to 1200 m at the center of the baiyun sag and punctuated by rapid subsidence and uplift events the baiyun event was manifested in the study area by a short lived uplift event in 23 9 23 3 ma followed by a short lived rapid subsidence in 23 3 19 8 ma in the central study area this localized rapid subsidence caused northward jump and anti clockwise rotation of the shelf break two order teeterboard seesaw like subsidence was observed in the study area in the post rifting stage suggesting elastic deformations of the crust and lithosphere c 2014 elsevier b v all rights reserved

seismic geomorphology architecture and genesis of miocene shelf sand ridges in the pearl river mouth basin northern south china sea abstract multiple stages of large scale shelf sand ridges including the shoreface attached and the offshore types have developed in the miocene successions on the mid shelf region of the pear river mouth basin northern south china sea utilizing a high quality 3d seismic data set accompanying 2d seismic profiles and well logs the morphology architecture and genesis of these shelf sand ridges have been systematically investigated in this study the ridges are of very large scale with the largest one having a maximum height of 64 m a width of more than 20 km and a length of 37 km within the 3d survey area being mound shaped they also display obvious asymmetry character with the ridge crest preferentially located on the se side three main internal components including the ridge front central ridge and the ridge tail have been recognized through careful anatomy analysis of the two most well imaged ridges each displaying distinct expressions on seismic amplitudes and geometries in the plan view most of the shelf sand ridges are generally ne sw oriented and widening to the sw direction scouring features can also be clearly observed along the sw direction including scour depressions and linear sandy remnants on well logs the shelf sand ridges are represented by an overall coarsening upward pattern intervals with blocky sandstones are preferentially present on higher locations due to a differential winnowing process controlled by shelf topography plenty of evidence indicates that these ridges were primarily formed by the reworking of forced regressive or lowstand deltaic deposits under a persistent southwesterly flowing current during the subsequent transgression this very current is a composite one which is speculated to consist of winter oceanic current scsbk south china sea branch of kuroshio intrusion onto the shelf and internal waves propagating from the luzon strait tidal currents might have contributed to the se growth of the ridge in response to the reglaciation of antarctic ice sheet and the closure of pacific indian ocean seaway in the middle miocene the intensification of the north pacific western boundary current was considered to have potential links to the initiation of the shelf sand ridges at 12 ma the development of shelf ridges was terminated and replaced by rapid deltaic progradation at 5 5 ma

depositional and structural evolution of the middle miocene depositional episode east central gulf of mexico a regional stratigraphic and structural framework has been established for the middle miocene sediment depositional episode from the shelf through the slope to the basin floor for the east central gulf of mexico two widespread transgressive deposits associated with the faunal tops amphistegina b 15 5 ma and textularia w 12 1 ma define the middle miocene depositional episode the middle miocene episode incorporates four genetic cycles each 1 2 m y bounded by regional maximum flooding surfaces and distal condensed sections two long lived extrabasinal fluvial deltaic axes the ancestral mississippi and the eastern tennessee systems provided the bulk of sediments that infilled the middle miocene depocenters salt related structural provinces controlled the location and configuration of the depocenters linked structural systems dominated by gravity spreading and an eastern minibasin province driven by differential subsidence were established during this period two depositional systems tracts characterize the constructional shelf margin of the middle miocene 1 a volumetrically dominant mixed load fluvial dominated platform delta shelf margin delta and delta fed apron systems tract and 2 a strand plain shelf and muddy slope systems tract however the offlapping shelf margin systems were punctuated by a large scale slope failure the harang collapse system associated with massive salt withdrawal and retreat of delta systems a large volume of sediment funneled by the harang collapse system bypassed the slope initiating a long lived submarine fan system the fan formed in a minibasin corridor and unconfined abyssal plain approximately 240 mi 384 km from the active shelf margins the fan system evolved from a structurally controlled elongate sand rich to mixed sand and mud fan to a large radial mixed sand and mud fan

late triassic batang group arc volcanic rocks in the northeastern margin of qiangtang terrane northern tibet partial melting of juvenile crust and implications for paleo tethys ocean subduction the batang group btg volcanic rocks in the zhiduo area with nw trending outcrops along the northeastern margin of the qiangtang terrane northern tibet are mainly composed of volcaniclastic rocks dacite and rhyolite major and trace element sr and nd isotope zircon u pb and hf isotope data are presented for the btg dacites laser ablation inductively coupled plasma mass spectrometry zircon u pb dating constrains the timing of volcanic eruption as late triassic 221 1 ma major and trace element geochemistry shows that the btg volcanic rocks are classified as calc alkaline series all samples are enriched in large ion lithophile elements and light rare earth elements with negative slightly positive eu anomalies eu eu 0 47 1 15 and depleted in high field strength elements and heavy rare earth elements in addition these rocks possess less radiogenic sr 87sr 86sr i 0 7047 0 7078 much radiogenic nd end t 4 2 to 1 3 and hf ehf t 4 0 6 6 isotopes suggesting that they probably originated from partial melting of a crustal source containing a mantle derived juvenile component the inferred magma was assimilated by crustal materials during ascending and experienced significant fractional crystallization by combining previously published and the new data we propose that the btg volcanic rocks were genetically related to southwestward subduction of the ganzi litang ocean a branch of paleo tethys in the northeastern margin of the qiangtang terrane given the coeval arc affinity magmatic rocks in the region we envisage that the ganzi litang ocean may extend from the zhongdian arc through the yidun terrane to the zhiduo area probably even further northwest to the tuotuohe area

blueschist bearing metamorphic core complexes in the qiangtang block reveal deep crustal structure of northern tibet a 500 km long belt of metamorphic exposures in the qiangtang block provides an opportunity to study the internal structure of northern tibetan crust metamorphic rocks exposed at two widely separated areas along this belt consist of blueschist bearing melange and are bounded by late triassic early jurassic domal low angle normal faults we propose that this melange was underplated to the qiangtang block and was subsequently exhumed by detachment faulting both the underplating and the exhumation occurred during early mesozoic southward subduction of oceanic lithosphere along the jinsha suture this model predicts that the deeper crust of much of northern tibet consists of accretionary melange in contrast to the continental crystalline crust of southern tibet and may account for north south variations of cenozoic tectonism in tibet

permo carboniferous sequences of gondwana affinity in southwest china and their paleogeographic implications abstract in southwest china permo carboniferous depositional sequences of gondwana affinity were first discovered in the himalayan region by the expedition team of acadimia sinica in 1975 by 1983 gondwana affinity permo carboniferous sequences had been identified also in the lhasa block the south qiangtang block in tibet and the tengchong and baoshan blocks in yunnan these sequences are characterised by the presence of successions which are interpreted as glacio marine deposits and by the presence of gondwana affinity biota the distribution of gondwana affinity permo carboniferous indicates that basins whose remnants are now represented by the yarlung zangbo suture and the bangong nujiang suture did not exist at that time and the vast area south of the lungmu shuanghu jinshajiang zone in tibet and west of the changning menglian belt in yunnan formed a part of the northern margin of gondwana

lithospheric and upper mantle structure of the northeastern tibetan plateau 1 we use receiver functions calculated for data collected by the indepth iv seismic array to image the three dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern tibet our results indicate an average crustal thickness of 65 to 70 km in northern tibet in addition we observe a 20 km moho offset beneath the northern margin of the kunlun mountains a 10 km moho offset across the jinsha river suture and gently northward dipping moho beneath the qaidam basin a region in the central qiangtang terrane with higher than normal crustal vp vs ratio of 1 83 can be the result of the eocene magmatic event in the qiangtang terrane we observe a significant lithospheric mantle discontinuity beneath the bangong nujiang suture at 80 km depth which dips 10 to the north reaching 120 km depth we interpret this feature as either a piece of lhasa terrane or remnant oceanic slab underthrust below northern tibet we detect a 20 km depression of the 660 km discontinuity in the mantle transition zone beneath the northern lhasa terrane in central tibet which suggests this phase transition has been influenced by a dense and or cold oceanic slab a modest 10 km depression of the 410 km discontinuity located beneath the northern qiangtang terrane may be the result of localized warm upwelling associated with small scale convection induced by the penetration of the sinking indian continental lithosphere into the transition zone beneath the central tibetan plateau

u pb zircon age geochemical and lu hf isotopic constraints of the southern gangma co basalts in the central qiangtang northern tibet abstract a recent study suggests that the central qiangtang is a key locality to investigate the evolution of the opening and closure of the paleo tethys ocean basalts are commonly associated with supercontinent fragmentation and they have the potential to indicate the tectonic environment into which they were erupted in this study laser ablation inductively coupled plasma mass spectrometry la icp ms u pb zircon dating whole rock geochemistry and zircon hf isotope analysis were used to study newly discovered basalts in the southern gangma co area of central qiangtang dating of magmatic zircons from three basalt samples indicates that the basalts erupted in the late devonian to early carboniferous early tournaisian at 360 350 ma the basalts are geochemically similar to within plate basalts and formed from a depleted mantle source we suggest that the basalts may have been a product of the breakup of the northern margin of gondwana in the late devonian to early carboniferous 360 350 ma which may be linked to the initial rifting and opening of the paleo tethys ocean in the qiangtang area

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

nearshore along strike variability is the concept of the systems tract unhinged sequence stratigraphic models assume that nearshore strata have relatively consistent and laterally persistent stacking at the systems tract scale and therefore may not fully describe the three dimensional stratigraphic architecture in areas displaying marked nearshore along strike variability a stratigraphic model of nearshore deposits is presented that corrects for this assumption by explaining variations in along strike stratal geometries in terms of a systematic change in the orientation of a shoreline trend or clinoform rollover a scenario comparable to deflection around a hinge the model defines hinge zones that are both fixed and moving with respect to time and was created from outcrop well log and seismic reflection data model end members predict contemporaneous progradational aggradational and retrogradational stacking bounded by surfaces displaying significant along strike changes in architecture implying that sequence stratigraphic surfaces can be diachronous we advocate examining the impact of stratigraphic variations parallel to depositional strike by testing for the presence of uniform versus differential progradation phenomena responsible for creating unhinged and hinged nearshore depositional systems respectively understanding these differences will improve subsurface predictions and provide a more complete understanding of the stratigraphic evolution of sedimentary basins

accommodation succession δa δs sequence stratigraphy observational method utility and insights into sequence boundary formation the future of sequence stratigraphy depends on stratigraphers making observations with a common method so that physical frameworks can be clearly separated from interpretations of driving mechanisms depositional sequence boundary selection is a well known controversy that could be resolved with objective recognition criteria accommodation succession sequence stratigraphy refines traditional methods using sedimentary facies facies associations vertical stacking stratal geometries and stratal terminations as the objective record of competing rates of accommodation change and sediment fill through time observations are placed in context of lateral transgression and regression and vertical aggradation and degradation movement of shoreline through time across multiple timescales in hierarchal stacks the repeating motif consists of a subaerial unconformity and its correlative subaqueous surface overlain in coastal settings by a basinward shift in coastal onlap and strata with progradational to aggradation stacking then retrogradation and aggradation progradation degradation stacking these stacking patterns are bounded by key surfaces recognized by stratal terminations and characteristic vertical successions of facies this pattern is independent of time duration or position on a sea level curve but incorporates data resolution regional extent and hierarchal stacking examples from multiple datasets show the utility and objectivity of the method and provide insights into sequence boundary formation

early ordovician granites from the south qiangtang terrane northern tibet implications for the early paleozoic tectonic evolution along the gondwanan proto tethyan margin abstract early ordovician granites occur in the gemuri and bensong co areas of the south qiangtang terrane northern tibet and la icp ms zircon u pb dating reveals that the magmatism took place between 486 and 480 ma the geochemical features of these early ordovician granites are comparable to those of high k calc alkaline s type granites they exhibit negative values of zircon ehf t 8 5 to 1 7 and whole rock end t 8 1 to 0 5 as well as old zircon hf model ages tcdm 1349 1992 ma and whole rock nd model ages tcdm 1145 1804 ma these early ordovician granites can be attributed to partial melting of the paleoproterozoic metasedimentary rocks of the south qiangtang terrane while minor amounts of mantle derived components were introduced into their magma sources taking into account previous data we propose that the early ordovician granites developed in a post collisional tectonic setting and that they were related to the collisional accretion of asian microcontinental fragments such as the south china north china tarim and qaidam kunlun terranes that took place as a result of oceanic subduction along the gondwana proto tethyan margin during the early paleozoic

origin and pre cenozoic evolution of the south qiangtang basement central tibet abstract the qiangtang terrane in central tibet with its high pressure rocks is a key area to unravel the evolution of the paleo tethys we present a new 1 50 000 map of the rongma area in the central qiangtang terrane of which relatively little is known so far we show that the qiangtang metamorphic belt can be separated in a paleozoic autochthonous basement and an overlying allochthonous thrust stack of subduction melange that contains high pressure rocks and permian sediments detrital zircon ages youngest peak at 591 ma and an 470 ma granite intrusion age constrain the age of the qiangtang basement to be between the late precambrian to middle ordovician this is in agreement with the observed unconformity between basement and overlying mid late ordovician strata this unconformity and the zircon age spectra are comparable to the himalaya area the qiangtang terrane must thus have been part of the gondwana supercontinent during the early paleozoic the occurrence of the late triassic eclogite and glaucophane bearing schists in the central qiangtang terrane indicates the existence of a suture zone between the north and south qiangtang terranes before the late triassic this suture zone resulted from closure of the paleo tethys between the north and south qiangtang terranes late triassic syn collisional granites and rapidly exhumed high pressure rocks resulted from the closure of this ocean and final amalgamation of the re united qiangtang terranes with eurasia collision of the lhasa and qiangtang terranes is correlated with north dipping reverse faults in the south qiangtang terrane which were probably related to exhumation of the qiangtang basement and formation of the qiangtang culmination

early palaeozoic orogenesis along the indian margin of gondwana tectonic response to gondwana assembly abstract shrimp u pb dating of zircons from a peralkaline s type lesser himalayan granite from the kathmandu region nepal indicate an age of emplacement of 475 ma the granites along with metasedimentary xenoliths show a similar signature of inherited detrital zircon ages ranging from archaean to early palaeozoic with prominent late mesoproterozoic grenvillian and neoproterozoic pan african age peaks and have a maximum age of 500 ma based on the youngest detrital grains deformation structures in xenoliths are truncated by the granite and along with the granites are assigned to a cambro ordovician orogenic event herein termed the bhimphedian orogeny that can be traced across the himalaya from pakistan to the eastern himalaya and possibly extends west into afghanistan we interpret the orogeny as being related to andean type orogenic activity on the northern margin of the indian continent following gondwana assembly the magmatic arc was associated with andesitic and basaltic volcanism and was active from c 530 to 490 ma the arc activity overlaps with and is succeeded by regional deformation crustal melting and s type granite emplacement that extended to 470 ma orogenic activity was driven by coupling across the plate margin either during on going subduction or through accretion of microcontinental ribbons possibly represented by the lhasa and qiangtang blocks it represents the termination of an orogenic cycle termed the north indian orogen that commenced with neoproterozoic rifting and passive margin development and terminated with the bhimphedian orogeny this was succeeded by a return to passive margin setting along the northern indian margin of gondwana which continued until the cenozoic himalayan orogeny

erratum to revised tectonic forecast of global shallow seismicity based on version 2 1 of the global strain rate map in our previous article bird and kreemer 2015 we presented a set of six long term stationary forecasts of global shallow seismicity identified as the model series shift gsrm2a f as preliminary validation we also presented retrospective tests against global shallow seismicity in the years 2005 2012 as recorded in the global centroid moment tensor catalog a smoothed seismicity forecast computed by yan kagan and david jackson kagan and jackson 1994 2010a b 2011 2014 was

zircon u pb hf isotopes and whole rock geochemistry of gneissic granites from the jitang complex in leiwuqi area eastern tibet china record of the closure of the paleo tethys ocean abstract previous investigations have indicated that the changning menglian cmsz and longmu co shuanghu lssz suture zones represent the paleo tethys ocean of northern tibet and western yunnan of china respectively however our understanding of the paleo tethys suture zone in eastern tibet seems to be incomplete the north lancangjiang suture zone nlsz has been hypothesized to mark the paleo tethys ocean in eastern tibet the present study reports new zircon u pb ages and hf isotope data and whole rock major and trace element data from the gneissic granites from the jitang complex in the leiwuqi area of the nlsz in order to verify this hypothesis six samples of gneissic granites yielded weighted mean 206 pb 238 u ages of 249 237 ma the geochemical data show that the gneissic granites are characterized by high sio 2 70 79 77 75 wt k 2 o 2 00 6 13 wt low a cnk values hf t values from 2 7 to 2 5 and t c dm model ages 1447 1009 ma indicate that they were generated by the partial melting of the meso proterozoic juvenile crust these gneissic granites were interpreted to have formed in the post collisional tectonic setting related to the closure of the paleo tethys ocean by combining previously published and the new data we propose that the nlsz connects the lssz and cmsz in the tibetan plateau and marks a paleo tethys ocean basin in eastern tibet

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

volcanic rocks of the 1985 tibet geotraverse lhasa to golmud volcanic rocks encountered during the tibet geotraverse have been studied in the field in thin section and by major and trace element geochemistry in order to determine their most probable original eruptive environment rocks from a total of eleven distinct volcanic provinces were studied in this way they provide evidence for an active continental margin or post collision province of probable devonian early carboniferous age in the northern kunlun mountains an active continental margin of late carboniferous age in the southern lhasa terrane permian continental rifts in the central qiangtang and central kunlun terranes triassic volcanic arcs in the southern lhasa and northern qiangtang terranes a triassic active continental margin dyke swarm in the northern kunlun mountains a jurassic post collision or back arc rifting province in the southern qiangtang terrane a jurassic island arc in the northern lhasa terrane a cretaceous post collision province in the northern lhasa terrane possibly extending into the southern qiangtang terrane and a palaeogene active continental margin in the southern lhasa terrane an oligocene trachyte plug in the northern qiangtang terrane was the only evidence encountered during the geotraverse of volcanism post dating the palaeogene india eurasia collision however the composition of this plug coupled with new and published analyses from miocene volcanics in the southern lhasa terrane and from the pliocene recent volcanic province of northwest tibet places important constraints on models for post collision underplating of tibet by continental lithosphere any underplating is likely to have been a much later than the start of collision b directed beneath tibet from the north as well as the south and c limited in extent

contrasting rift and subduction related plagiogranites in the jinshajiang ophiolitic melange southwest china and implications for the paleo tethys 1 the jinshajiang ophiolitic melange zone in southwest china represents a remnant of the eastern paleo tethys ocean field geochronological and geochemical studies have identified two distinct suites of plagiogranites within the melange the dongzhulin trondhjemite and jiyidu tonalite which represent rift and subduction settings respectively related to opening and closing of the ocean shrimp u pb analysis on zircons extracted from the dongzhulin trondhjemite yields a mean 206pb 238u age of 347 7 ma ree and isotopic characteristics suggest an origin from low pressure partial melting of an amphibolitic protolith highly variable hf isotopic compositions for zircons from this body may indicate a heterogenous source involving both depleted mantle and enriched continental components this together with geologic relations suggests formation near an embryonic spreading center in a continent ocean transition setting the jiyidu tonalite has a u pb zircon age of 283 3 ma and geochemical data indicates high sr y la yb n nb ta and low y and marked heavy ree depletion these signatures suggest derivation from low degree partial melting of subducted slab at pressure high enough to stabilize garnet and rutile a slab melt origin is also supported by in situ hf and o data for zircon that show isotopic compositions comparable with typical altered oceanic crust thus the crystallization age of the jiyidu high sr y tonalite provides a constraint for the subduction of the jinshajiang ocean floor the rift related dongzhulin trondhjemite and subduction related jiyidu high sr y tonalite constrain the timing and setting of opening and closing of this segment of the paleo tethys ocean

petrogenesis and tectonic setting of triassic granitoids in the qiangtang terrane central tibet evidence from u pb ages petrochemistry and sr nd hf isotopes abstract triassic granitoids including the 220 ma shuanghu and 210 ma rongma granitoids studied here are widely distributed around the longmu shuanghu suture and in the qiangtang terrane central tibet the majority of these granitoids can be classified as high k calc alkaline in nature and yield negative ba and sr anomalies on primitive mantle normalized diagrams in addition they are enriched in light rare earth elements lree la yb n 1 61 21 79 strongly enriched in large ion lithophile elements lile e g cs rb and k and depleted in high field strength elements hfse e g nb and ti magma mixing played a role in the genesis of the shuanghu granodiorites as indicated by the occurrence of dioritic enclaves and the wide range in zircon hf compositions ehf t 15 0 to 2 5 the i type shuanghu granodiorites and s type shuanghu and rongma granites might have been derived from melting of southern qiangtang crust given the high initial sr 0 7131 0 7272 low end t 8 9 to 11 1 and zircon ehf t values 15 to 7 2 the granitoids may have formed during melting of southern qiangtang crust heated by upwelling asthenosphere mantle a result of break off and delamination of the paleo tethys slab in a collisional setting

towards a sequence stratigraphic solution set for autogenic processes and allogenic controls upper cretaceous strata book cliffs utah usa upper cretaceous strata exposed in the book cliffs of east central utah are widely used as an archetype for the sequence stratigraphy of marginal marine and shallow marine deposits their stratal architectures are classically interpreted in terms of accommodation controls that were external to the sediment routing system allogenic and that forced the formation of flooding surfaces sequence boundaries and parasequence and parasequence set stacking patterns processes internal to the sediment routing system autogenic and allogenic sediment supply controls provide alternatives that can plausibly explain aspects of the stratal architecture including the following 1 switching of wave dominated delta lobes expressed by the internal architecture of parasequences 2 river avulsion expressed by the internal architecture of multistorey fluvial sandbodies and related deposits 3 avulsion generated clustering of fluvial sandbodies in delta plain strata 4 autoretreat owing to increasing sediment storage on the delta plain as it lengthened during progradation expressed by progradational to aggradational stacking of parasequences 5 sediment supply control on the stacking of and sediment grain size fractionation within parasequence sets the various potential allogenic controls and autogenic processes are combined to form a sequence stratigraphic solution set this approach avoids anchoring of sequence stratigraphic interpretations on a specific control and acknowledges the non unique origin of stratal architectures

middle miocene climate cooling linked to intensification of eastern equatorial pacific upwelling during the middle miocene earth s climate transitioned from a relatively warm phase miocene climatic optimum to a colder mode with reestablishment of permanent ice sheets on antarctica thus marking a fundamental step in cenozoic cooling carbon sequestration and atmospheric co2 drawdown through increased terrestrial and or marine productivity have been proposed as the main drivers of this fundamental transition we integrate high resolution 1 3 k y benthic stable isotope data with x ray fluorescence scanner derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive recovered at integrated ocean drilling program site u1338 to reconstruct eastern equatorial pacific productivity variations and to investigate temporal links between high and low latitude climate change over the interval 16 13 ma our records show that the climatic optimum 16 8 14 7 ma was characterized by high amplitude climate variations marked by intense perturbations of the carbon cycle episodes of peak warmth at southern hemisphere insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean a switch to obliquity paced climate variability after 14 7 ma concurred with a general improvement in carbonate preservation and the onset of step wise global cooling culminating with extensive ice growth over antarctica ca 13 8 ma we find that two massive increases in opal accumulation ca 14 0 and ca 13 8 ma occurred just before and during the final and most prominent cooling step supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial pacific contributed to co2 drawdown

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