the role of india asia collision in the amalgamation of the gondwana derived blocks and deep seated magmatism during the paleogene at the himalayan foreland basin and around the gongha syntaxis in the south china block abstract southeast asia comprises collage of continental blocks that were rifted out in phases from the northern parts of the gondwanic indo australian continent during the paleozoic mesozoic time and were accreted through continental collision process following closure of the paleo and neo tethys the south china and indo china blocks were possibly rifted during early palaeozoic whereas the tibetan and sibumasu blocks were rifted during permo carboniferous when the said margin was under glacial and or cool climatic condition the indo burma andaman iba sikule lolotoi blocks were also rifted from the same indo australian margin but during late jurassic this was followed by break up of the indian and the australian continents during early cretaceous the opening of the indian ocean during the tertiary was synchronous with closing of the tethys india asia collision during early middle eocene was a mega tectonic event apart from initiating the himalayan orogeny and the eastward strike slip extrusion of the indochina block from the southeast asian continental collage along the ailao shan red river shear zone it also caused early mid eocene continental flood basalt activity in the himalayan foreland basin indian continent s post collisional indentation induced syntaxial buckling of asian continental collage at its eastern end possibly caused late paleogene highly potassic magmatism around the gongha syntaxial area that was located close to the sutured margin of south china continent with indochina block at the outer fringe of namche barwa syntaxis these magmatic bodies are soon after left laterally displaced by the ailao shan red river shear zone the nature and chemistry of magma at these two settings indicate that both groups result from similar petrogenetic and tectonic processes representing deep seated melts due to mantle decompression some deep faults produced at the edge of flexed indian continental lithosphere and responsible for the development of the foreland basin may have produced continental flood basalt and related magma by decompressional melting of enriched sub continental mantle the site specific location and time sequence of magmatism from the marginal parts of south china continent and located at the outer fringe of namche barwa syntaxis are strongly significant it suggests that these magmatic bodies may also be genetically related to the india asia collision process and indentation induced syntaxial buckling of upper mantle beneath the marginal parts of the south china rigid continent

shrimp zircon u pb geochronology geochemistry and sr nd hf isotopic compositions of a mafic dyke swarm in the qiangtang terrane northern tibet and geodynamic implications abstract regional mafic dyke swarms are commonly emplaced in extensional tectonic settings and are typically considered to be linked with continental break up a large number of mafic dykes areal extent of 40 000 km 2 have recently been documented in the middle of the qiangtang terrane northern tibet zircon u pb isotope analyses using a sensitive high resolution ion microprobe shrimp indicate that the dykes were emplaced in the early permian 279 2 ma 283 1 ma 285 1 ma and 285 3 ma whole rock geochemical data show that the qiangtang mafic dykes are tholeiitic in composition and exhibit relative enrichment in light rare earth element lree and depletion in nb ta and ti resembling continental intra plate basalts whole rock sr nd and zircon hf isotopic data suggest that mafic dyke magma was derived from a depleted mantle source e nd t 5 1 to 7 6 and e hf t 4 9 to 14 8 the chemical and isotopic characteristics make the mafic dykes similar to the panjal traps and permian basalts in the tethyan himalayas the contemporaneous and widespread emplacement of ca 283 ma continental intra plate basaltic rocks in the qiangtang terrane and in the himalayas is suggestive of a large igneous province lip this lip is linked to the initial rifting and opening of the meso tethys ocean during the permian

tectonic significance of the lambert graben east antarctica reconstructing the gondwanan rift antarctica s lambert graben australia s north west shelf and the eastern indian peninsula all host thick fault bounded permian triassic successions these terranes were adjacent to each other in gondwana the lambert graben intersects the modern coastline strikes oblique to shelf architecture and has a geophysical signature that can be traced 1000 km inland vitrinite reflectance data from the graben margins record permian triassic infill australia s north west shelf is the relict of an intracontinental carboniferous permian rift that was infilled during the permian triassic then driven to oceanic completion during jurassic cretaceous gondwana breakup this rift was compartmentalized over length scales of 650 km corresponding to accommodation zones margin normal geophysical lineaments and long lived crustal weaknesses in eastern india similar compartmentalization is marked by extensive coal bearing graben systems gondwana reconstructions indicate that the lambert graben corresponds to the orientation and length scale of carboniferous permian rift compartmentalization the lambert graben represents an accommodation zone of a wide intracontinental rift that extended from australia s north west shelf between india and antarctica to southern africa this rift collected gondwana s thick permian triassic sedimentary blanket and rich alluvial coal deposits

first report of lower permian basalts in south tibet tholeiitic magmatism during break up and incipient opening of neotethys abstract the neo tethys ocean began to form at early permian times when continental flood basalts were emplaced in various areas of the newly formed indian passive margin exposed today in the so called tibetan sedimentary zone of the himalaya lower permian mafic volcanic rocks which have long been known from various himalayan localities from kashmir to arunachal pradesh are here for the first time reported to occur also in south tibet bhote kosi basalts of the gyirong county the basalts unconformably overlie lowermost permian diamictites with locally intervening black shales and debris flow deposits and are followed in turn by chert bearing quartzarenites and silty to phosphatic marls yielding brachiopods of roadian wordian age the age of the lavas can thus be bracketed as late early permian post sakmarian and pre roadian the geochemistry of these subalkalic tholeiites akin to morbs testifies to their similarity not only with the adjacent nar tsum spilites of central nepal but also with the panjal traps and abor volcanics of the western and eastern himalayas respectively the geochemical signature of lower permian volcanic rocks is in fact uniform all along the himalayan range and markedly different from that of basaltic rhyolitic alkalic products sporadically emplaced during the previous rifting stage rift volcanism in the tethys himalaya began in the early carboniferous and came to an end in sakmarian times in the early permian initial submergence of the rift shoulders and sediment starvation were followed by tholeiitic magmatism which is therefore interpreted as following break up and incipient sea floor spreading in the neotethys ocean roughly contemporaneous emplacement of continental flood basalts of similar geochemical signature along a 2000 km long rift axis would in fact suggest extensive mantle melting at the transition from continental rifting to break up and opening of the neotethys between northern gondwana and the peri gondwanian blocks

multiscale seismic reflectivity of shallow thermoclines seismic oceanography is coming of age as an established technique of observation of the thermohaline structure of the ocean the present paper deals with the seismic reflectivity of the armorican shelf seasonal thermocline west of france based on two seismic experiments performed with a sparker source the peak frequency was 500 hz for the aspex experiment where the thermocline was located at 27 m water depth and reduced to 400 hz associated to a higher source level for the ifosismo experiment where the thermocline was 12 m deeper despite this settings only the first experiment could clearly highlight the thermocline reflector providing the first seismic observation of a shallow oceanic structure to better understand the limitation of high resolution seismic devices in detecting weak oceanic features we develop a wavelet based seismic analysis and consider as a first approximation a simple thermocline modelled by a gauss error function allowing an analytical expression for the associated seismic reflectivity we show that the acoustic impedance profile of the thermocline is mainly controlled by a sound velocity proportional to the temperature we show that the seismic reflectivity is controlled by the reflection coefficient of the large scale structure of the thermocline and by an attenuation factor which depends on the ratio between the seismic wavelength and the characteristic size of the thermocline depending on this ratio the strength of the thermocline related reflection may be too weak to be detected by seismic measurement

effect of seismic source bandwidth on reflection sections to image water structure 1 the seismic reflection profile is the convolution of the seismic acquisition impulse response and the target impedance contrasts in the ocean these contrasts are mainly determined by the widths and gradients of the temperature transitions between the different water masses hence seismic oceanography profiles are sensitive to the frequency bandwidth of the seismic acquisition system we tested a novel seismic source that allowed us to simultaneously profile the ocean with differing impulse responses we show that frequencies 20 hz are best to delineate large impedance contrasts that occur over a vertical scale of several tens of meters whereas frequencies 80 hz image the boundaries of layers of around 10 m we demonstrate a towed acquisition system that can operate from a research vessel to give a bandwidth from 10 to 120 hz that could if required be modified to provide frequencies up to 200 hz

mapping turbidity layers using a combination of high resolution seismic oceanographic and physical oceanographic data synchronized seismic and oceanographic data were acquired during the geophysical oceanography go project cruise in the gulf of cadiz in april may 2007 the small volume 117 cu in mini gi gun seismic source used during the go calibration experiment provided high resolution seismic data which unveiled new features of the internal structure of the ocean the seismic acquisition design gave a usable bandwidth of 50 250 hz with a vertical resolution of 1 25 m which is similar to that achieved by co located ctd casts we focus on the reflections observed on seismic data covering the moorings area to test the hypothesis that measurable reflections can be generated by suspended sediment we perform forward modeling of seismic response based on the temperature salinity and light attenuation measurements available from ctd casts forward modeling based solely on temperature and salinity profiles show that thermohaline structure does not always explain reflections in water column but they are consistent

middle permian plume related magmatism of the hawasina nappes and the arabian platform implications on the evolution of the neotethyan margin in oman 1 permian pillow basalts are commonly found in oman either at the base of the hawasina nappes or within the arabian platform successions exposed in the saih hatat tectonic window there is an ongoing debate on whether these lavas include normal mid oceanic ridge basalts nmorb witnessing the permian opening of the neotethys or if they are plume related magmas that are emplaced either on the arabian platform or on its thinned continental margin we sampled these lavas from several paleontologically dated middle permian sites four of them buday ah rustaq al ajal and wadi wasit are located within the hawasina nappes and are exposed as thrust slices overlain by the samail nappe and one wadi aday is within the arabian platform units and is exposed in the saih hatat window these lavas are associated with marine sediments deposited in environments ranging from proximal saih hatat wadi wasit and base of the thrust pile of al ajal to distal buday ah rustaq and top of the al ajal pile with respect to the arabian platform major and trace element features of the basalts allow two groups to be recognized enriched high ti basalts similar to alkali basalts from intracontinental traps rifted continental zones and oceanic islands are exposed in wadi aday wadi wasit and at the structural base of the al ajal pile moderately enriched to slightly depleted low ti tholeiitic basalt magmas resembling the low ti flood basalts and those from seaward dipping reflector sequences are represented in wadi al hulw in saih hatat buday ah rustaq and at the top of the al ajal thrust pile both groups show distinct plume related trace element signatures and they do not include typical nmorb although emplaced in shallow to deep submarine environments these basalts provide no direct evidence for a neotethyan seafloor spreading event in the hawasina basin instead they were likely erupted through the crust of the already rifted and drowned arabian continental margin thus despite their characteristic plume related geochemical signatures the middle permian basalts from oman were not likely emplaced during the evolution of a typical volcanic rifted margin we suggest that they originated from a mantle plume which ascended beneath the arabian passive margin well after the initiation of seafloor spreading of the neotethys

the permian fusulinoidean faunas of the sibumasu and baoshan blocks their implications for the paleogeographic and paleoclimatologic reconstruction of the cimmerian continent abstract permian fusulinoidean faunas occur in mainly four stratigraphic levels in the baoshan block of west yunnan and the sibumasu block of southeast asia which constituted part of the eastern cimmerian continent the oldest fauna from the upper part of the dingjiazhai formation in the baoshan block consists of pseudofusulina eoparafusulina and a new boultoniid genus and is assignable to the yakhtashian artinskian the second one which occurs in the basal part of the ratburi limestone and its equivalent strata in the sibumasu block is represented by monodiexodina and is probably referable to the bolorian kungurian the third fauna composed of eopolydiexodina rugososchwagerina yangchienia chusenella jinzhangia and several other genera is dated to the murgabian wordian and occurs in the lower part of the shazipo and daaozi formations in the baoshan block and the main part of the ratburi limestone in the sibumasu block the youngest fauna of probably dzhulfian wuchiapingian age is found in the upper part of the ratburi limestone and contains nanlingella reichelina codonofusiella and a few staffellid genera a smaller foraminiferal genus shanita found from the upper part of the ratburi limestone and the upper part of the shazipo formation is also an important element of the foraminiferal assemblage near the midian dzhulfian capitanian wuchiapingian boundary in the baoshan and sibumasu blocks in the eastern cimmerian continent low generic diversity throughout the permian and the paucity of tethys characterizing neoschwagerinid and verbeekinid genera during middle permian time are two remarkable features of the permian fusulinoidean faunas in the cimmerian continent the generic diversity of permian fusulinoidean faunas in space and time gradually increases from the early permian to late middle permian as well as from the eastern cimmerian areas to western ones the temporal increase of the generic diversity can be explained by the northward drift of the cimmerian continent during permian time in contrast the lower generic diversity of the eastern cimmerian permian fusulinoidean faunas against western ones is possibly due to an oblique arrangement of the continent to paleolatitude thus the western cimmerian continent was more proximal to the tropical tethyan domain than its eastern part in addition the middle permian cimmerian paleobiogeographic region is likely to be subdivided into two subregions the western tethyan cimmerian and the eastern gondwanan cimmerian based on the distribution pattern of verbeekinid and neoschwagerinid fusulinoideans and overall generic diversity the scarce occurrence or total absence of these essentially tethys indicating fusulinoideans in the baoshan and sibumasu blocks suggests that the eastern cimmerian continent was still far from the equatoro tropical cathaysian domain and was probably in a warm temperate or subtropical zone until the end of the permian the eastern cimmerian areas finally migrated into a tropical zone by the late triassic judging from well developed carnian sponge coral buildups in the chaiburi formation in the sibumasu block

ocean internal wave spectra inferred from seismic reflection transects 1 internal waves affect many important dynamical processes in the ocean but in situ observations of internal waves are infrequent and spatially sparse here we show that remote sensing of internal waves by marine seismic reflection methods can provide quantitative information on internal wave energy and its spatial variability at high lateral resolution and full ocean depth over large volumes of the ocean seismic images of the norwegian sea water column show reflections that capture snapshots of finestructure displacements due to internal waves horizontal wave number spectra derived from digitized reflection horizons in the open ocean compare favorably to the garrett munk tow spectrum of oceanic internal wave displacements spectra within 10 km laterally and 200 m vertically of the continental slope show enhanced energy likely associated with internal wave sloping boundary interactions

geochemical characteristics of the abor volcanic rocks ne himalaya india nature and early eocene magmatism the abor volcanic rocks exposed in the siang window ne himalaya occur as dismembered thrust hound packages interbanded with fossiliferous shelf sediments of upper palaeocenc to middle eocene age their age is broadly contemporaneous with the age of collision between the indian and tibetan continents they were therefore erupted in a convergent setting through channel ways in the leading edge of the indian continent the volcanic rocks occur beneath the lesser himalayan thrust sheets and were transported with them during their southward propagation the abor volcanic rocks were erupted in an early palaeogene shallow basin located within marginal parts of the himalayan fold thrust belt south of the collision zone they may thus represent foreland basin magmatism the abundances of some major and large ion lithophile elements have been affected by alteration of the samples ti and some other trace elements remain unaffected however and their abundances indicate that the volcanic rocks form a chemically coherent group of tholciites and alkalinc basalts the tholeiitic and alkaline basalts reflect different degrees of melting and low pressure fractional crystallization involving olivine and plagioclase has played a significant role in the evolution of the basalts on the basis of ratios of strongly incompatible elements the two basalt types appear to have been generated from sources having similar character this source is inferred to he enriched sub continental mantle

multifrequency seismic detectability of seasonal thermoclines assessed from argo data seismic oceanography is a developing research topic where new acoustic methods allow high resolution teledetection of the thermohaline structure of the ocean first implementations to study the ocean surface boundary layer have recently been achieved but remain very challenging due to the weakness and shallowness of such seismic reflectors in this article we develop a multifrequency seismic analysis of hydrographic data sets collected in a seasonally stratified midlatitude shelf by argo network floats to assess the detectability issue of shallow thermoclines this analysis for which sensitivity to the data reduction scheme used by argo floats for the transmission of the profiles is discussed allows characterizing both the depth location and the frequency dependency of the dominant reflective feature of such complex structures this approach provides the first statistical distribution of the range of variability of the frequency dependent seismic reflection amplitude of the midlatitude seasonal thermoclines we introduce a new parameter to quantify the overall capability of a multichannel seismic setup including the source strength the fold and the ambient noise level to detect shallow thermoclines seismic source signals are approximated by ricker wavelets providing quantitative guidelines to help in the design of seismic experiments targeting such oceanic reflectors for shallow midlatitude seasonal thermoclines we show that the detectability is optimal for seismic peak frequencies between 200 and 400 hz this means that airgun and sparker sources are not well suited and that significant improvements of source devices will be necessary before seismic imaging of osbl structures can be reliably attempted

permian climatic and paleogeographic changes in northern gondwana the khuff formation of interior oman abstract detailed stratigraphic paleontologic and petrographic data from the middle permian khuff formation exposed in the haushi huqf area of interior oman provide new insight into the permian climatic evolution of the northern gondwana margin and on the still debated timing of neotethys opening between gondwana and the cimmerian blocks the khuff formation is interpreted to record a major transgression of neotethyan waters in wordian times middle permian at a stage of full oceanization and tectonic quiescence when thermal subsidence caused final drowning of rift shoulders and deposition of marine carbonates onto vast portions of stable arabia the petrographic composition of middle permian sandstones indicates a post rift stage and documents a long term increase in mineralogic stability ascribed to a shift toward warm humid climatic conditions coupled with reduced relief and longer transit times of detritus from source to basin raising temperatures and northward latitudinal drift towards lower tropic latitudes throughout the permian are fully documented by rich transitional marine faunas and available paleomagnetic evidence

seismic reflection imaging of water mass boundaries in the norwegian sea 1 results from the first joint temperature and seismic reflection study of the ocean demonstrate that water mass boundaries can be acoustically mapped multichannel seismic profiles collected in the norwegian sea show reflections between the norwegian atlantic current and norwegian sea deep water the images were corroborated with a dense array of expendable bathythermographs and expendable conductivity temperature depth profiles delineating sharp temperature gradients over vertical distances of 5 15 m at depths over which reflections occur fine structure from both thermohaline intrusions and internal wave strains is imaged low amplitude acoustic reflections correspond to temperature changes as small as 0 03 c implying that seismic reflection methods can image even weak fine structure

updated gondwana permian cretaceous earth history of australia abstract permo carboniferous glaciation confined to icecaps and mountain glaciers was followed by permian coal measures and early triassic barren measures and redbeds in the east terminally deformed in the mid triassic coal deposition resumed during the late triassic and tholeiite was erupted in the southeast after rifting the western margin was formed by the opening of the indian ocean at 156 and 132 ma at 140 ma a brief glaciation affected central australia by the 99 ma mid cretaceous the southern margin was finally shaped by the opening of the southeastern indian ocean the shoreline retreated to the present coast from the maximum aptian shoreline of an epeiric sea and the eastern highlands were uplifted to produce the present morphology of australia new data relate to the permo carboniferous and early cretaceous glaciations the kiaman reversed paleomagnetic interval events about the permian triassic boundary including possible impact craters advances in palynology invertebrate paleontology macrofloral paleontology and paleobiogeography the provenance of sediments by u pb ages and host rock affinity of zircons stable isotopes and biomarkers in petroleum systems coal environments calibrating the time scale with u pb ages of zircons fission track thermotectonic imaging geothermal energy and terranes split off the western margin

waveform preserving processing flow of multichannel seismic reflection data for adjoint state full waveform inversion of ocean thermohaline structure this paper presents a specific data processing flow to be applied to marine multichannel seismic reflection data collected by a streamer in order to use them to perform prestack adjoint waveform inversion of ocean s thermohaline properties the overall goal is to increase the signal to noise ratio snr of the weak reflections generated at the small impedance contrasts within the water layer while preserving the direct wave the processing flow focuses on increasing the snr of the shot gather records by forcing noise amplitudes to fall inside a range of physical plausible values for water layer reflections this processing step is applied in two independent branches of the workflow one dealing with the water layer reflections and the second with the direct wave which are separated by applying a singular value decomposition to test the performance of the processing flow we combine actual noise field recordings with a synthetic seismic data set we apply the proposed data processing flow to quantify differences between noise free and processed record sections and we then compare with the results obtained by applying a butterworth filter bf for offsets smaller than 1500 m the bf processing produces a signal with snr 0 1 the proposed workflow allows to retrieve the seismic signal with 0 1 snr 2 4 for offsets larger than 1500 m the bf processing allows obtaining the snr up to 1 4 while the proposed workflow increases the snr up to 5 we finally demonstrate that the processed data can be used to perform waveform inversion with an accuracy of 0 02 m s

the youngest marine deposits preserved in southern tibet and disappearance of the tethyan ocean abstract fossil ages as young as priabonian 38 34 ma are reported for the last marine sedimentary rocks in southern tibet correlation is based on examination of foraminifers and nannofossil biostratigraphy of youngest preserved sediments in sections at gamba zongpu tingri qumiba as well as a previously unreported section at yadong our results demonstrate that a marine seaway remained in existence south of the yarlung tsangpo suture zone until at least priabonian time notably this remains a maximum age estimate in this area as all sections are truncated by erosion or faulting we compare our results with sections throughout the himalaya region to demonstrate that shallow marine conditions existed widely during the eocene period in fact it seems likely that the marine conditions in the tethyan himalaya did not entirely disappear by the end of priabonian especially in the eastern himalaya the data presented in this study place direct constraints on the elimination of the tethyan ocean and thus have important implications for timing of the india eurasia collision

structures and timing of permian rifting in the central oman mountains saih hatat abstract we investigated remnants of permian rifting sequences in the saih hatat metamorphic window central oman mountains part of the former arabian continental margin which has been overthrust by the semail ophiolite in the less deformed northwestern part of the saih hatat well preserved or inverted syn sedimentary normal faults indicate ene wsw permian extension we propose new stratigraphic correlations with the more deformed and metamorphosed parts of the saih hatat based on lithostratigraphy and large scale structures unfolding which indicate that breakup of the permian platform resulted in sediment thickening and deepening towards the ene this rift event was coeval with within plate volcanism that was widespread in all compartments of the margin but marked by a single event in the stratigraphic record of the platform in this part of the arabian margin rifting was restricted to a short time interval less than 5 my during the murghabian and volcanism can be correlated with the panjal traps event we propose that this part of the neotethyan margin formed as a volcanic rifted margin in a triple junction setting

imaging meddy finestructure using multichannel seismic reflection data 1 this work illustrates the great potential of multichannel seismic reflection data to extract information from the finestructure of meddies with exceptional lateral resolution 10 15 m we present seismic images of three meddies acquired in the gulf of cadiz sw iberian peninsula which consist of concentric reflectors forming oval shapes that sharply contrast with the background oceanic structure the seismic images reveal the presence of different regions within the meddies that are consistent with those observed in historical temperature t and salinity s data the core region characterized by smooth t and s variations is weakly reflective the double diffusive upper and lower boundaries and the lateral interleaving outer edges characterized by stronger t and s contrasts display strong reflectivity bands these new observations clearly show differences between layers developed at the upper and lower boundaries that can contribute to the knowledge of mixing processes and layering formation in oceans

high resolution seismic imaging of the ocean structure using a small volume airgun source array in the gulf of cadiz a small volume 117 cu inch seismic source producing signal predominantly in the 150 200 hz frequency window was used during the go calibration experiment in the gulf of cadiz april may 2007 the data show the small scale 10 m in the z direction internal structure of the ocean high resolution images display seismic reflectors that often appear as distinct horizontal short a few hundred meters to a few km long segments lying at different depths while low resolution 20 to 30 hz display long horizontal reflectors a few tens of km sometimes linked by short apparently dipping segments the present data suggest that this apparent dipping effect is due to the insufficient separation power 4 of the low resolution data improving high resolution acquisition systems hence appears to be a critical challenge to understand the seismic response of the ocean

origin and assembly of the tethyside orogenic collage at the expense of gondwana land abstract the tethysides are a superorogenic complex flanking the eurasian continent to the south and consisting of the cimmerides and alpides products of palaeo and neo tethys respectively we here review their evolution mainly on the basis of new maps showing the distribution of sutures magmatic rocks certain palaeobiogeographically and palaeoclimatologically significant taxa and facies and fragments of pan african 900 450 ma orogenic system forming the basement of many tethyside blocks these are supplemented by palaeomagnetic data reported in the literature a fundamental tenet of this paper is that major sutures which contain ophiolite fragments represent tectonic sections between continental blocks where oceanic crust has been subducted palaeo tethys came into existence largely in late carboniferous time coevally it began to be consumed by both internal and peripheral subduction zones which continued into the permian some of these had been inherited from pre tethyan times in the later permian rifting subparallel with the northern margin of gondwana land began between the zagros and malaysia separating a cimmerian continent from n gondwana land and thus heralding the opening of neo tethys and other smaller oceans that were back arc basins of palaeo tethys this rifting possibly also extended farther west into crete and mainland greece however the north china block yangtze block huanan block the eastern moity of the qangtang block north tibet and annamia all originally pieces of the end proterozoic early palaeozoic gondwana land had already separated from it in pre late carboniferous times possibly during the devonian all of these blocks and the cimmerian continent were characterized by cathaysian floral elements in late palaeozoic time palaeomagnetic and palaeontological data showing the original gondwana land affinity of these continental blocks are supplemented by correlating late proterozoic early palaeozoic pan african sutures orogenic belts and sedimentary basin fragments across tethyside sutures late permian foraminiferal provinces are related to this palaeogeographical interpretation by triassic times most cimmeride subduction zones were already in existence the cimmerian continent accelerated its separation from gondwana land and locally in the late permian began disintegrating internally along the waser rushan pshart banggong co nu jiang mandalay ocean by late triassic time all of the chinese blocks except lhasa and annamia had collided with each other and with laurasia the resulting enormous orogenic collage had a soft cushion between itself and laurasia in the form of the enormous accretionary complex of the songpan ganzi this connection enabled laurasian land vertebrates to reach south east asia by late triassic time in late triassic to middle jurassic times most major cimmeride collisions were completed widespread aridity in central asia occurred in late jurassic time probably in the rain shadow of the newly formed cimmeride mountain wall neo tethyan subduction systems formed along the s margin of the cimmerides or within neo tethyan oceanic lithosphere during the jurassic most if not all were north or east dipping they continued the northerly migration of the tethyside blocks evolution of the tethysides influenced the distribution of marine and terrestrial organisms and affected sea level changes and patterns of atmospheric circulation during much of the mesozoic and cainozoic it is likely to have reflected the surface expression of a persistent trend in the large scale convective circulation in the mantle that continuously transported material northward into the tethyan domain

apparent polar wander paths for the major continents 200 ma to the present day a palaeomagnetic reference frame for global plate tectonic reconstructions summary synthetic apparent polar wander apw paths for north america south america eurasia india central africa australia and antarctica for the last 200 myr are proposed computation of these apw paths is based upon the latest version 4 5a of the global paleomagnetic database gpmdb a revised global plate tectonic model since the early jurassic and a new technique for generating smoothed apw paths the smoothing technique includes the following steps 1 pre selection of palaeopoles including pre filtering parameters number of sites number of samples per site 95 per cent confidence circle about mean direction cleaning procedure and time uncertainty 2 generation of palaeolatitude and declination plots for a reference site on each continent that combines palaeopoles via a global plate tectonic circuit 3 independent spline regression analyses of the palaeolatitude and declination plots 4 removal of palaeolatitude or declination data that deviate by more than 10 from the regression curves post filtering process 5 generation of synthetic apw paths from the resulting palaeolatitude and declination plots these synthetic apw paths are then rotated into african coordinates to determine the best fit apw path and a global palaeomagnetic reference frame four representative plate tectonic reconstructions and global plate velocity fields are presented for the three time intervals that correspond to globally synchronous changes in plate motion

stratigraphic implications of palaeomagnetic data from honduras summary palaeomagnetic results from mainly cretaceous rocks in honduras delineate a distinctive apparent polar wander path apwp which is well suited for magnetostratigraphy the apwp is based on palaeomagnetic data from palaeontologically dated units in the established stratigraphic column and three radiometrically dated intrusions the ages and stratigraphic positions of sedimentary units whose stratigraphic assignments have been debated can be inferred by comparing their palaeornagnetic pole postion with the known apwp the results demonstrate the usefulness of magnetostratigraphy for resolving stratigraphic problems in the absence of fossils or marker beds and for areas of discontinuous exposures for regional interpretations the most important conclusion is that strata in honduras that have been assigned to the todos santos formation were not deposited on the same tectonic plate as the todos santos formation of guatemala and southern mexico there is no evidence that the honduran todos santos strata are depositionally related to the true todos santos formation the name todos santos formation should be abandoned in honduras and for the entire chortis block

himalaya the northern frontier of east gondwanaland abstract the himalayan province which represents the northern platform of the peninsular india belonging to east gondwanaland was strongly affected by pan african diastrophism 500 25 ma ago this brought to an end the protracted purana cycle of sedimentation throughout the peninsular india and the lesser himalaya and interrupted basin filling in its northern tethyan domain but the sea returned in the early permian along a narrow depression formed due to rifting of the himalayan crust in what is today the southern lesser himalaya in the rift valley was deposited tillites by glaciers of the gondwana continent under grip of refrigeration along with the glacigene conglomerates were emplaced diamictites generated by submarine slides triggered presumably by earthquakes originating from faults delimiting the rift the diamictities are admixed with lava agglomerate and tuff indicating widespread volcanism in the rift valley the rifting culminated in the breaking away of the tibetan part of the himalaya in the late permian and formation of neotethys between the gondwanaland and the cimmerian microcontinent embodying tibet iran and turkey rivers of the northern peninsular india flowed in the northerly directions since the middle proterozoic through early eocene in the late eocene there was a drastic drainage reversal to south and southeast when the himalaya emerged in the northern front of the gondwanaland

an early bird from gondwana paleomagnetism of lower permian lavas from northern qiangtang tibet and the geography of the paleo tethys abstract the origin of the northern qiangtang block and its late paleozoic early mesozoic drift history remain controversial largely because paleomagnetic constraints from pre mesozoic units are sparse and of poor quality in this paper we provide a robust and well dated paleomagnetic pole from the lower permian kaixinling group lavas on the northern qiangtang block this pole suggests that the northern qiangtang block had a paleolatitude of 21 9 4 7 s at ca 296 9 1 9 ma these are the first volcanic based paleomagnetic results from pre mesozoic rocks of the qiangtang block that appear to average secular variation accurately enough to yield a well determined paleolatitude estimate this new pole corroborates the hypothesis first noted on the basis of less rigorous paleomagnetic data the presence of diamictites detrital zircon provenance records and faunal assemblages that the northern qiangtang block rifted away from gondwana prior to the permian previous studies have documented that the northern qiangtang block accreted to the tarim north china continent by norian time we calculate a total northward drift of ca 7000 km over ca 100 myr which corresponds to an average south north plate velocities of 7 0 cm yr our results do not support the conclusion that northern qiangtang has a laurasian affinity nor that the central qiangtang metamorphic belt is an in situ paleo tethys suture our analysis however does not preclude paleogeographies that interpret the central qiangtang metamorphic belt as an intra qiangtang suture that developed at southernly latitudes outboard of the gondwanan margin we emphasize that rigorous paleomagnetic data from carboniferous units of northern qiangtang and especially upper paleozoic units from southern qiangtang can test and further refine these paleogeographic interpretations

temperature contrasts in the water column inferred from amplitude versus offset analysis of acoustic reflections 1 we show that seismic amplitude versus offset avo analysis can be used to remotely quantify the temperature contrasts responsible for acoustic reflections in the ocean we inferred the sound speed and density contrasts associated with two reflections in the norwegian sea by comparing their avo response to that predicted by the zoeppritz equations estimates of temperature contrasts were calculated from sound speed contrasts using wilson s equation and compared with in situ temperature measurements from coincident expendable bathythermographs xbts a strong reflection from line 9 is best explained by a 6 m s step in sound speed corresponding to a temperature decrease of 1 5 c a weaker reflection from line 11 yielded a sound speed contrast of 1 2 m s corresponding to a temperature decrease of 0 3 c the inferred temperature contrasts match those found in xbt data remarkably well l1 norm misfits between predicted and calculated values indicate that the acoustic impedance contrasts are principally controlled by sound speed contrasts rather than density contrasts avo analysis offers an accurate and robust technique for estimating sound speed and therefore temperature contrasts in the water column

gondwana to asia plate tectonics paleogeography and the biological connectivity of the indian sub continent from the middle jurassic through latest eocene 166 35 ma abstract using the most up to the date information available we present a considerably revised plate tectonic and paleogeographic model for the indian ocean bordering continents from gondwana s middle jurassic break up through to india s collision with asia in the middle cenozoic the landmass framework is then used to explore the sometimes complex and occasionally counter intuitive patterns that have been observed in the fossil and extant biological records of india madagascar africa and eastern eurasia as well those of the more distal continents although the paleogeographic model confirms the traditional view that india became progressively more isolated from the major landmasses during the cretaceous and paleocene it is likely that at various times minor physiographic features principally ocean islands provided causeways and or stepping stone trails along which land animals could have migrated to from the sub continent aside from a likely link albeit broken by several marine gaps to africa for much of this time it is notable that the present day recent biota of madagascar indicates that the ancestors of five land mammal orders plus bats crossed the 400 km wide mozambique channel at different times in the cenozoic it is possible that the kerguelen plateau connected india and australia antarctica in the mid cretaceous approximately 115 90 ma later the seychelles mascarene plateau and nearby elevated sea floor areas could have allowed faunas to pass between southern india and madagascar in the late cretaceous from around 85 65 ma with an early cenozoic extension to this path forming as a result of the reunion hot spot trace islands growing on the ocean floor to the ssw of india the modelling also suggests that india s northward passage towards asia with eventual collision at 35 ma involved the ne corner of the sub continent making a glancing contact with sumatra followed by burma from 57 ma late paleocene onwards a scenario which is compatible with the fossil record indicating that india asia faunal exchanges began occurring at about this time finally we contend that a number of biologically based direct terrestrial migration routes that have been proposed for last 15 m y of the cretaceous asia to india antarctica to madagascar and or india can probably be dismissed because the marine barriers likely varying from 1000 up to 2500 km were simply too wide

late artinskian early kungurian early permian warming and maximum marine flooding in the east gondwana interior rift timor and western australia and comparisons across east gondwana abstract substantial new information is presented on upper artinskian kungurian deposits in timor leste and in the canning southern carnarvon and northern perth basins of western australia these basins situated between about 35 s and 55 s palaeolatitude formed part of the east gondwana interior rift a precursor to the rift that 100 my later formed the indian ocean in this region timor lay near the main axis of the east gondwana interior rift whereas the western australian basins were marginal splays from the rift axis the main depocentres developed as a result of faulting that was initiated during the late pennsylvanian detailed lithostratigraphic and biostratigraphic analyses have been made on the newly recognized bua bai limestone and the type cribas group in timor the noonkanbah formation in the canning basin the byro group in the merlinleigh sub basin of the southern carnarvon basin and the carynginia formation in the northern perth basin in timor the succession which is highly disrupted by faulting was deposited under open marine conditions probably in a shelf basin setting restricted very shallow water seas flooded the canning basin and the merlinleigh byro irwin sub basins of the southern carnarvon and northern perth basins and had highly variable oxygen levels and salinities typical of estuarine environments a similar pattern of warming and bathymetric change is recognized in all studied basins during the early part of the late artinskian cool conditions prevailed with water temperatures 0 4 c forming sea ice in the merlinleigh byro irwin rift rapid warming during the latter part of the late artinskian was accompanied by maximum marine flooding close to the artinskian kungurian boundary climatic and bathymetric conditions then allowed carbonate mounds with larger fusulines and a variety of algae to develop in the northern part of the rift system and tubiphytes conodonts and brachiopods with tethyan affinities to migrate into the marginal rift basins despite the generally adverse water quality at these depositional sites comparison between the stratigraphic record from the east gondwana interior rift and coeval records from lhasa and sibumasu indicate a similar pattern of climate change during the carboniferous to end cisuralian similar trends probably are present in eastern australia although there is confusion over the correlation of some units

seismic reflection imaging of shallow oceanographic structures 1 multichannel seismic mcs reflection profiling can provide high lateral resolution images of deep ocean thermohaline fine structure however the shallowest layers of the water column z 150 m have remained unexplored by this technique until recently in order to explore the feasibility of shallow seismic oceanography so we reprocessed and analyzed four multichannel seismic reflection sections featuring reflectors at depths between 10 and 150 m the influence of the acquisition parameters was quantified seismic data processing dedicated to so was also investigated conventional seismic acquisition systems were found to be ill suited to the imaging of shallow oceanographic structures because of a high antenna filter effect induced by large offsets and seismic trace lengths and sources that typically cannot provide both a high level of emission and fine vertical resolution we considered a test case the imagery of the seasonal thermocline on the western brittany continental shelf new oceanographic data acquired in this area allowed simulation of the seismic acquisition sea trials of a specifically designed system were performed during the aspex survey conducted in early summer 2012 the seismic device featured i four seismic streamers each consisting of six traces of 1 80 m ii a 1000 j sig sparker source providing a 400 hz signal with a level of emission of 205 db re 1 pa 1 m this survey captured the 15 m thick 30 m deep seasonal thermocline in unprecedented detail showing images of vertical displacements most probably induced by internal waves

physicochemical processes in the magma chamber under the black mountain porphyry cu au deposit philippines insights from mineral chemistry and implications for mineralization the black mountain porphyry cu au deposit in the baguio district northern luzon philippines is associated with late miocene to pliocene intrusive rocks that retain primary crystallization signatures providing an excellent natural laboratory to study the details of magma chamber processes each igneous phase contains disequilibrium textures including resorptive textures in plagioclase and distinct core rim textures in amphibole high crystallization temperatures and pressures in felsic 880 c and 2 8 kbar and mafic 1 030 c and 7 7 kbar rocks recorded by amphibole phenocrysts reflect crystallization in the magma chamber amphibole in felsic rocks aged 6 39 0 49 to 2 83 0 23 ma have similar crystallization temperatures and pressures suggesting a long lived and hot felsic magma chamber under the black mountain deposit four independent oxybarometers including amphibole coexisting magnetite ilmenite magmatic anhydrite and zircon consistently show a high oxidation state of nno 1 for the felsic magma and nno 0 7 for the mafic magma element profiles across phenocrystic plagioclase display repeated oscillatory variations of ca fe and sr contents with large anorthite variations and a positive correlation between cao and feo the amphibole is classified as group 1 mg hornblende to tschermakite hornblende in felsic rocks and group 2 mg hastingsite in mafic rocks the group 1 amphiboles show a variety of major and trace element variations from core to rim in disequilibrated grains and transitional compositions to group 2 mg hastingsite both mineral textures and chemistry recorded by phenocrysts of plagioclase and amphibole indicate repeated mafic magma recharge in the felsic magma chamber the common occurrence of rounded or elongated sulfide inclusions in the megacrystic amphibole from the mafic rocks 2 81 0 15 ma suggests a greater enrichment of cu in mafic rocks relative to the ore forming porphyries 2 91 2 83 ma this is also consistent with higher cu contents 3 4 0 9 ppm in the megacrystic amphibole from the mafic rocks relative to amphibole in felsic rocks 1 0 0 2 ppm and may indicate up to 3 4 times higher cu in the mafic magma relative to felsic magma therefore large scale mafic magma recharge particularly at 2 8 ma likely introduced ore forming metals to the long lived felsic magma chamber further contributing to the fertility of the felsic rocks and ultimately to cu au mineralization at the black mountain deposit

evolution of the himalayan paleogene foreland basin influence of its litho packet on the formation of thrust related domes and windows in the eastern himalayas a review abstract eocene oligocene foreland basin was formed in response to the india asia collision and ensuing himalayan orogenesis the initial collision during late paleocene to early eocene was broadly contemporaneous laterally the paleogene sediments although discontinuously exposed are remarkably similar in their character and organization in the eastern himalayas it is virtually concealed tectonically but is exposed close to and beneath the main boundary thrust mbt as narrow but laterally extensive thrust slivers of fossiliferous eocene sediments lateral continuity and similar marine fauna in them establish the presence of thicker eocene sediments beneath mbt further north several domes and windows in the eastern himalayan frontal belt have evolved with similar geometry the largest siang window exposes duplex antiform of paleogene sediments and volcanics at the core which have arched up the mbt roof thrust the latter underlies passively domed up late plaeozoic and proterozoic himalayan thrust packets the cores of other windows mainly expose low grade proterozoic rocks with or without the late paleozoic rocks a similar sequence of pre tertiary thrust packet is exposed to the south in the frontal belt which override the neogene sediments across mbt a buried basement indenture of the indian continent continues beneath the siang window located at the eastern himalayan syntaxis the cores of other windows are possibly arched up by the duplexes of pre tertiary and tertiary sediments during the process of southward movement of the crystalline and foreland sheets

thermohaline fine structure in an oceanographic front from seismic reflection profiling we present acoustic images of oceanic thermohaline structure created from marine seismic reflection profiles across the major oceanographic front between the labrador current and the north atlantic current the images show that distinct water masses can be mapped and their internal structure imaged using low frequency acoustic reflections from sound speed contrasts at interfaces across which temperature changes the warm cold front is characterized by east dipping reflections generated by thermohaline intrusions in the uppermost 1000 meters of the ocean our results imply that marine seismic reflection techniques can provide excellent spatial resolution of important oceanic phenomena including thermohaline intrusions internal waves and eddies

paleomagnetic data support early permian age for the abor volcanics in the lower siang valley ne india significance for gondwana related break up models confusion exists as to the age of the abor volcanics of ne india some consider the unit to have been emplaced in the early permian others the early eocene a difference of 230 million years the divergence in opinion is significant because fundamentally different models explaining the geotectonic evolution of india depend on the age designation of the unit paleomagnetic data reported here from several exposures in the type locality of the formation in the lower siang valley indicate that steep dipping primary magnetizations mean 72 7 6 2 equating to a paleo latitude of 58 1 are recorded in the formation these are only consistent with the unit being of permian age possibly artinskian based on a magnetostratigraphic argument plate tectonic models for this time consistently show the ne corner of the sub continent 50 s in the early eocene it was just north of the equator which would have resulted in the unit recording shallow directions the mean declination is counter clockwise rotated by 94 around half of which can be related to the motion of the indian block the remainder is likely due local himalayan age thrusting in the eastern syntaxis several workers have correlated the abor volcanics with broadly coeval mafic volcanic suites in oman ne pakistan nw india and southern tibet nepal which developed in response to the cimmerian block peeling off eastern gondwana in the early middle permian but we believe there are problems with this model instead we suggest that the abor basalts relate to india antarctica india australia extension that was happening at about the same time such an explanation best accommodates the relevant stratigraphical and structural data present day position within the himalayan thrust stack as well as the plate tectonic model for permian eastern gondwana

stratigraphy and sedimentary history of the nepal tethys himalaya passive margin abstract the sedimentary history of the nepal tethys himalaya began with deposition of thick carbonates in the cambro ordovician followed by a mixed siliciclastic carbonate epicontinental succession recording two major deepening events in the early silurian and late devonian fossiliferous carbonate ramp deposits in the tournaisian were disconformably followed by white quartzose sandstones and black mudrocks with locally intercalated diamictites derived from sedimentary rocks and deposited in asymmetric tectonic basins rift stage break up in the mid early permian locally associated with effusion of tholeiitic lava flows was followed by a transgressive sandy to shaly locally coal bearing or bioclastic unit capped by condensed pelagic carbonates in the middle to late permian juvenile ocean stage subsidence of the cooling stretched crust led close to bathyal water depths in the olenekian but then slowed down in the middle triassic to increase again sharply in the late triassic owing to renewed extensional tectonic activity and sediment loading during up and out building of the indian continental terrace deposition of tropical platform carbonates finally became widespread in the middle liassic mature passive margin stage the initial fragmentation of gondwana in the middle jurassic led to rejuvenation of the indian craton and deposition of quartzo feldspathic hybrid arenites capped by condensed oolitic ironstones deposited at warm subtropical latitudes in the late bathonian middle callovian next a discontinuous pelagic grey marly limestone unit was followed by the ammonoid rich offshore spiti shale in the late jurassic the final disintegration of gondwana began in the berriasian when quartzose siliciclastics derived again from the rejuvenated indian craton and partly from recycling of older clastic successions were followed by thick deltaic to shelf volcaniclastics documenting eruption of alkali basalts in the valanginian followed in the hauterivian to albian by more felsic differentiates such as the trachyandesites exposed in the lesser himalaya 120 km to the south a widespread drowning episode fostered by waning volcaniclastic supply during a global eustatic rise is documented by a major glauconitic horizon deposited at middle southern latitudes in the late albian overlain by scaglia like pelagic limestones in the latest albian the final part of sedimentary history during the rapid northward flight of india and its collision with eurasia is not documented anywhere in nepal due to later erosion of upper cretaceous to lower tertiary strata

an alternative plate tectonic model for the palaeozoic early mesozoic palaeotethyan evolution of southeast asia northern thailand burma abstract an alternative model for the geodynamic evolution of southeast asia is proposed and inserted in a modern plate tectonic model the reconstruction methodology is based on dynamic plate boundaries constrained by data such as spreading rates and subduction velocities in this way it differs from classical continental drift models proposed so far the different interpretations about the location of the palaeotethys suture in thailand are revised the tertiary mae yuam fault is seen as the emplacement of the suture east of the suture we identify an indochina derived terrane for which we keep the name shan thai formerly used to identify the cimmerian block present in southeast asia now called sibumasu this nomenclatural choice was made on the basis of the geographic location of the terrane eastern shan states in burma and central thailand and in order not to introduce new confusing terminology the closure of the eastern palaeotethys is related to a southward subduction of the ocean that triggered the eastern neotethys to open as a back arc due to the presence of late carboniferous early permian arc magmatism in mergui burma and in the lhasa block south tibet and to the absence of arc magmatism of the same age east of the suture in order to explain the presence of carboniferous early permian and permo triassic volcanic arcs in cambodia upper triassic magmatism in eastern vietnam and lower permian middle permian arc volcanites in western sumatra we introduce the orang laut terranes concept these terranes were detached from indochina and south china during back arc opening of the poko song ma system due to the westward subduction of the palaeopacific this also explains the location of the cathaysian west sumatra block to the west of the cimmerian sibumasu block

two dimensional mapping of fine structures in the kuroshio current using seismic reflection data 1 multi channel seismic reflection data acquired in the pacific ocean off the muroto peninsula of shikoku island japan reveal the two dimensional distribution of fine structures in the kuroshio current eighty one seismic sections each extending 80 km perpendicular to the current and separated by 100 m were acquired from 20 june to 15 august 1999 57 days the seismic data clearly show that fine structures extend over 40 km perpendicular to the current in almost all of the profiles a simulation study using acoustic model from ctd data demonstrates that fine structure of temperature and salinity identified in ctd data acquired from the kuroshio current off the ashizuri peninsula yield a synthetic seismic profile with characteristics similar to the muroto transect profiles

fine scale thermohaline ocean structure retrieved with 2 d prestack full waveform inversion of multichannel seismic data application to the gulf of cadiz sw iberia this work demonstrates the feasibility of 2d time domain adjoint state acoustic full waveform inversion fwi to retrieve high resolution models of ocean physical parameters such as sound speed temperature and salinity the proposed method is first described and then applied to pre stack multi channel seismic mcs data acquired in the gulf of cadiz sw iberia in 2007 in the framework of the geophysical oceanography project the inversion strategy flow includes specifically designed data pre conditioning for acoustic noise reduction followed by the inversion of sound speed in the shotgather domain we show that the final sound speed model has a horizontal resolution of 70m which is two orders of magnitude better than that of the initial model constructed with coincident expendable bathy thermograph xbt data and close to the theoretical resolution of o temperature t and salinity s are retrieved with the same lateral resolution as sound speed by combining the inverted sound speed model with the thermodynamic equation of seawater and a local depth dependent t s relation derived from regional conductivity temperature depth ctd measurements of the national oceanic and atmospheric administration noaa database the comparison of the inverted t and s models with xbt and ctd casts deployed simultaneously to the mcs acquisition shows that the thermohaline contrasts are resolved with an accuracy of 0 18oc for temperature and 0 08 psu for salinity the combination of oceanographic and mcs data into a common pseudo automatic inversion scheme allows to quantitatively resolve submeso scale features that ought to be incorporated into larger scale ocean models of oceans structure and circulation this article is protected by copyright all rights reserved

indication for clockwise rotation in the siang window south of the eastern himalayan syntaxis and new geochronological constraints for the area palaeomagnetic rock magnetic and geochronological investigations were carried out on the abor volcanics of arunachal pradesh ne india a late palaeozoic formation age for part of the abor volcanics cannot be excluded based on k ar whole rock dating low temperature thermochronometers zircon u th he and fission track analyses yield a maximum burial temperature of c 150 170 8c during late miocene zft thermochronology of the yinkiong and miri fms indicates a post paleocene and post jurassic deposition age respectively this infers that the volcanic rocks intercalating or intruding them are not part of the late palaeozoic sequence but represent one or more latest cretaceous to tertiary event s therefore the abor volcanics are connected to at least two separate events of volcanism from palaeomagnetic sites two characteristic magnetic remanence components were separated a low coercivity component demagnetized below 20 mt and a high coercivity component demagnetized between 15 and 100 mt fold tests support a secondary origin of both components thermochronological and rock magnetic analyses indicate a low grade overprint event between india asia collision and miocene which probably represents the time of remanence acquisition the high coercivitycomponent shows a trend of clockwise declinations which is likely related to vertical axis rotations of the eastern himalayas due to eastward extrusion of the tibetan plateau the himalayan mountain range created by collision of the indian and eurasian continents during early eocene provides a unique opportunity for studying processes of continent continent collision yin harrison 2000 the himalaya extends between the nanga parbat syntaxis at the western end and the namche barwa syntaxis at the eastern end the area around the namche barwa syntaxis plays a key role in understanding geodynamic processes related to the eastward extrusion of the tibetan plateau ongoing indentation of india into eurasia has led to considerable tectonic deformation of the eurasian continent molnar tapponnier 1975 clockwise tectonic rotations in the eastern part of the himalayas are predicted by several numerical models and laboratory experiments in which the rigid indian plate penetrates into the continuum of asia e g houseman england 1993 beaumont et al 2001 cook royden 2008 palaeomagnetic investigations on cretaceous miocene rocks in the wider region north and west of the namche barwa syntaxis supported these clockwise rotations e g otofuji et al 1990 1998 funahara et al 1992 1993 huang opdyke 1993 sato et al 1999 2007 yang et al 2001 in addition velocity vectors obtained from global positioning system gps clearly display a clockwise rotational pattern around the namche barwa syntaxis for the present aseismic surface movements e g chen et al 2000 mattauer 2002 zhang et al 2004 shen et al 2005 sol et al 2007 most of the previous studies were performed north or east of the namche barwa syntaxis due to political and infrastructural restrictions and very dense vegetation the area south of the syntaxis is relatively unexplored the present study provides new from gloaguen r ratschbacher l eds growth and collapse of the tibetan plateau geological society london special publications 353 71 97 doi 10 1144 sp353 5 0305 8719 11 15 00 the geological society of london 2011 palaeomagnetic and geochronological data on the abor volcanic and adjacent sedimentary rocks of the siang window in arunachal pradesh ne india located just south of the namche barwa syntaxis the age of the abor volcanic rocks is highly controversial e g gansser 1964 jain thakur 1978 tripathi chowdhury 1983 bhat 1984 acharyya 1994 2007 kumar 1997 we present new geochronological and palaeomagnetic results that offer insight in the regional structure of the eastern himalayan syntaxis area and the extrusion of the tibetan plateau

permian carboniferous and permian triassic magmatism in the rift zone bordering the tethyan margin of southern pangea magma was emplaced in the india australia rift zone along the tethyan margin during permian carboniferous and permian triassic time permian carboniferous alkalic granite and basaltic and rhyolitic lava flows and tuffs formed at the same time as right lateral transtension of pangea as recorded by the magmatic rocks of neocratonic post variscan europe and post kanimblan eastern australia permian triassic tholeiitic basalt in india alkalic magmatic rocks in oman and rhyolite dolerite and undersaturated alkalic volcanic rocks in western australia preceded and accompanied the early opening of the neo tethys ocean coeval magmatism included the voluminous mid plate siberian traps the emeishan basalt of south china and the peak activity of the magmatic arc along the convergent panthalassan margin the background magmatism probably permitted the siberian traps to trigger the environmental catastrophe at the permian triassic boundary

a latest carboniferous warming spike recorded by a fusulinid rich bioherm in timor leste implications for east gondwana deglaciation abstract during the late paleozoic and early mesozoic timor lay in the northern part of the north south east gondwana rift system along which the western margin of australia later developed discovery of a latest gzhelian bioherm in the central highlands of timor leste has implications for latest carboniferous earliest permian climate history and deglaciation in basins further south in the rift system limestone outcrop of the maubisse formation near the village of kulau is recognized as a bioherm with a massive lower unit including reef framework at the base and a bedded grainstone upper unit the bioherm developed on a basalt substrate in warm shallow water as indicated by photozoan assemblages in the massive lower unit foraminifera belonging to 17 genera are recorded from the bioherm these include representatives of the families biseriamminidae biwaellidae bradyinidae cornuspiridae lasiodiscidae palaeotextulariidae pseudotaxidae ozawainellidae schubertellidae schwagerinidae staffellidae and textrataxidae twenty one species have been referred to known types and 12 species are left in open nomenclature the assemblage probably belongs within the uppermost gzhelian schwagerina robusta ultradaixina bosbytauensis zone although a possible lowest asselian correlation cannot be excluded the bioherm is the oldest carbonate unit so far recorded from the maubisse formation and the oldest sedimentary unit biostratigraphically dated in timor the dominantly heterozoan composition of the skeletal component of the limestone except for the basal photozoan assemblage and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40 s the late pennsylvanian was a time of glaciation that in australia is represented by a significant stratigraphic hiatus in basins to the south of timor in the east gondwana rift system the development of the kulau bioherm during the latest gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment alternating diamictite and mudstone in the southern basins

simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the kuroshio extension front 1 new simultaneous seismic reflection and physical oceanographic observations east of japan demonstrate the utility of the seismic reflection method in mapping oceanic fine structure synthetic seismograms calculated from temperature and salinity data confirm that seismic reflections correlate with physical oceanographic structures seismic reflections at the boundary between the warm kuroshio and the cold oyashio water masses correspond to well developed 10 m scale temperature fine structure vertical current profiles suggest that this fine structure is caused by interleaving of these two water masses we compare our seismic images with acoustic doppler current profiler adcp intensity maps and discuss similarities and the differences between seismic images and the adcp maps our study demonstrates that even relatively low energy seismic sources in this case a 3 4 l 210 in3 generator injector gi airgun can be used to image upper oceanic fine structure

full waveform inversion of reflection seismic data for ocean temperature profiles 1 we show that ocean temperature profiles can be accurately recovered using only acoustic methods employed at the sea surface using a towed air gun array and a hydrophone streamer thermohaline boundaries are ensonified at a suite of frequencies and angles yielding travel time trajectories and reflectivities these data are inverted via full waveform inversion to estimate sound speed and subsequently a temperature profile the high lateral data density of the seismic technique offers the potential of acoustically derived temperature profiles to be used to constrain models of ocean mixing and internal waves results on realistic synthetic data show that sound speed can be recovered with arbitrary accuracy when using broadband data with known source function and recording geometry application to field seismic data corroborated by expendable bathythermograph shows that even with a seismic acquisition system not specifically calibrated for seismic oceanography temperature contrasts within the ocean can be recovered to within one degree celsius

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

abor volcanics further evidence for the birth of the tethys ocean in the himalayan segment the himalayan region has a record of several phases of igneous activity which indicate a continued n s orientated tensional regime since at least late precambrian time though the earlier volcanic eruptions were restricted both in time and space the late carboniferous triassic activity was widespread in terms of both the time interval and area covered the abor volcanic activity in the eastern syntaxial bend of the himalayan fold belt is coeval with the initiation of late carboniferous triassic panjal trap volcanism of the western syntaxial bend and eruption of the sikkim lavas chemical characters of the abor volcanics indicate 1 a within plate rift tectonic setting of the lava eruptions 2 a transitional nature between tholeiitic and alkalic compositions 3 relative enrichment in incompatible elements and 4 high fe ti values similar to many such basalts erupted in the regions of active lithospheric rifting the olivine free nature a linear trend for mgo and low co contents of the studied rocks are suggestive of high pressure olivine fractionation for the generation of the bulk chemistry however large variations in the incompatible element abundances and ratios of rocks at a similar fractionation stage discount the evolution of the lava chemistry exclusively by simple fractionation or partial melting processes instead these characters together with the low zr nb ratio and within plate rift tectonic setting suggests the modification of an upper mantle source region possibly by fluid phase co 2 immediately before the partial melting and lithospheric rifting combining geology of the region with the geochemistry and inferred tectonic setting of these rocks the lava eruptions are suggested to have been associated with the 9rift valley stage9 of the tethys ocean formation in the present himalayan region

broadband receiver response from dual streamer data and applications in deep reflection seismology a method to process dual streamer data with under and over configuration is presented the method combines the results of dephase sum and dephase subtraction methods in the dephase methods the response of one streamer is time shifted so that the primary arrivals on both streamers are aligned and these responses are then summed or subtracted the method provides a broad spectral response from dual streamer data and increases the signal to noise ratio by a factor of 1 5 testing was done on synthetic data and then applied to a real data set collected by the british institutions reflection profiling syndicate birps its application to a deep seismic reflection data set from the british isles shows that the reflections from the lower crust contain frequencies up to 80 hz suggesting that some of the lower crustal reflectors may have sharp boundaries and could be 20 30 m thick

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

petrography and major element geochemistry of the permo triassic sandstones central india implications for provenance in an intracratonic pull apart basin abstract detrital mode composition of feldspars and heavy minerals and major element chemistry of sandstones from the permo triassic succession in the intracratonic satpura gondwana basin central india have been used to investigate provenance the talchir formation the lowermost unit of the succession comprises glacio marine and glacio fluvial deposits the rest of the succession base to top comprising the barakar motur bijori pachmarhi and denwa formations largely represent variety of fluvial depositional systems with minor fluvio deltaic and fluvio lacustrine sedimentation under a variety of climatic conditions including cold warm arid sub humid and semi arid qfl compositions of the sandstones indicate a predominantly continental block provenance and stable cratonic to fault bounded basement uplift tectonic setting compositional maturity of sandstones gradually increases upwards from the early permian talchir to the middle triassic denwa but is punctuated by a sharp peak of increased maturity in the barakar sandstones this temporal change in maturity was primarily controlled by temporal variation in fault induced basement uplift in the craton and was also influenced by climatic factors plots of different quartz types suggest plutonic source rocks for the talchir sandstones and medium to high rank metamorphic plus plutonic source rocks for the younger sandstones composition of alkali feldspars in the permo triassic sandstones and in different precambrian rocks suggests sediment derivation from felsic igneous and metasedimentary rocks compositions of plagioclase in the talchir and bijori sandstones are comparable with those of granite acid volcanic and metasedimentary rocks of the precambrian basement suggesting the latter as possible source rare presence of high k plagioclase in the talchir sandstones however indicates minor contribution from volcanic source rock exclusively plagioclase bearing metasedimentary rock tonalite gneiss and mafic rocks are the probable sources of plagioclase in the upper denwa sandstones quartz rich nature of the sandstones predominance of k feldspar over plagioclase and albite rich character of plagioclase in the sandstones is consistent with deposition in an intracratonic pull apart basin like the satpura gondwana basin composition of garnet and its comparison with that from the precambrian basement rocks suggests mica schist and amphibolite as possible sources predominance of dravite variety of tourmaline in the permian sandstones suggests sediment supply from metasedimentary rocks presence of both dravite and schorl variety of tourmaline in subequal amount in the triassic sandstones indicates sediment derivation from granitic and metasedimentary rocks however schorl bearing rocks are absent in the basement complex of the study area a cn k plot suggests granites acid volcanic rock and meta sediments of the basement as possible sources of the talchir sandstones and metasedimentary rocks for the barakar to pachmarhi sandstones the denwa sandstones were possibly derived from k feldspar free plagioclase bearing metasediments mafic rocks and tonalite gneiss chemical index of alteration cia values suggest low intensity source rock weathering for the talchir sandstones and higher intensity source rock weathering for the others various bivariate plots of major oxides composition of the sandstones suggest passive to active continental margin setting and even arc tectonic setting for a few samples

paleomagnetic and geochronological results from the zhela and weimei formations lava flows of the eastern tethyan himalaya new insights into the breakup of eastern gondwana