impact of india asia collision on se asia the record in borneo abstract borneo occupies a central position in the sundaland promontory of se asia it has a complex cenozoic geological history of sedimentation and deformation which began at about the same time that india is commonly suggested to have started to collide with asia some tectonic reconstructions of east and se asia interpret a large se asian block with borneo at its centre which has been rotated clockwise and displaced southwards along major strike slip faults during the cenozoic due to the indentation of asia by india however the geological history of borneo is not consistent with the island simply forming part of a large block extruded from asia the large clockwise rotations and displacements predicted by the indentor model for borneo are incompatible with palaeomagnetic evidence and there is no evidence that the major strike slip faults of the asian mainland reach borneo seismic tomography shows there is a deep high velocity anomaly in the lower mantle beneath se asia interpreted as subducted lithosphere but it can be explained just as well by alternative tectonic models as by the indentor model very great thicknesses of cenozoic sediments are present in borneo and circum borneo basins and large amounts of sediment were transported to the crocker turbidite fan of north borneo from the eocene to the early miocene but all evidence indicates that these sediments were derived from local sources and not from distant sources in asia elevated by india asia collision the cenozoic geological history of borneo records subduction of the proto south china sea and miocene collision after this ocean lithosphere was eliminated and a variety of effects resulting from long term subduction beneath se asia there is little to indicate that india asia collision has influenced the cenozoic geological record in borneo

kinematics of cenozoic extension on the south china sea continental margin and its implications for the tectonic evolution of the region abstract in the northern south china sea several large sedimentary basins developed during the cenozoic characterized by episodic rifting clockwise rotation of the rifts an eastward aging breakup unconformity and intensifying crustal extension to the east these features may be summarized by a scissors model the maximum rifting occurred north of the maximum thermal subsidence which was in turn north of the seafloor opening in contrast the nansha microcontinent south of the south china sea basin was dominated by compressional deformation during the cenozoic extension was of subordinate significance and manifested mainly by block faulting and tilting in the late early oligocene maximum tilting occurred in the southern part of the nansha microcontinent at distance from the deep sea basin of the south china sea the asymmetric development of extensional structures around the south china sea basin may be explained by the simple shear model proposed by wernicke 1981 the tectonic development of the south china sea was the consequence of various interactions of three major plates and may be summarized into three stages with dominating influences of respectively the retreat of the west pacific subduction zone in the late cretaceous the hard collision and impinging of india to tibet since the late eocene and the fast northward subduction of the indian ocean australian plate since the late early miocene

the wake of st vincent abstract the island of st vincent and the other windward islands in the southeastern caribbean were chosen as a field site for the study of weak mountain wakes by the authors definition a weak wake forms when the potential vorticity generated by a mountain is not strong enough to advect itself into eddies rather it is simply advected downstream by the ambient flow goes 8 and landsat sunglint images unambiguously revealed that the mountainous windward islands have remarkably long straight wakes the length of st vincent s wake exceeds 300 km although its width is only 20 km near the islands the wake structures reflect the details of the island topography these wakes do not exhibit any obvious diurnal effect boat surveys in the lee of st vincent confirmed the existence of features seen in the images the sharp wake boundary the small valley induced jet embedded in the near wake and the absence of any reverse flow aircraft surveys gave evidence of descent over the island and showed that the

the effect of bottom friction on shallow water flow past an isolated obstacle abstract the effect of bottom friction on fluid flow past an isolated obstacle is investigated in the shallow water framework the controlling parameter for this effect is the nondimensional bottom friction number defined as a ratio of friction to inertia with the bottom stress related to the horizontal wind via standard bulk aerodynamic formula the friction number is proportional to the surface roughness the horizontal scale of the obstacle and the inverse of the upstream fluid depth thus under otherwise identical conditions the flow past larger obstacles will be more viscous bottom friction modifies the vorticity generation in several ways but under normal conditions the wake formation remains dominated by a pseudoinviscid process related to the presence of hydraulic jumps however friction strongly controls the velocity deficit region of the wake and thus influences the stability of the steady state wakes predictions of the linear stability analysis are compared with numerical simulation

a revised jurassic radiolarian zonation for the south belt of the chichibu terrane western kyushu southwest japan abstract permian triassic and jurassic sedimentary and volcaniclastic rocks are distributed in the south belt of the chichibu terrane unfortunately they are not part of a sequence but are disordered masses of mappable units several sequences of jurassic age are found in the kuma massif on western kyushu the western part of the belt the radiolarian succession containing the sequences encompasses nearly the entire jurassic epoch detailed radiolarian successions from seven sections are discussed six sections consist mainly of bedded cherts and siliceous shales with minor terrigenous black shales one section consists of terrigenous black shales with oolitic limestone the radiolarian zonation presented here has been defined by the first and last appearances of age diagnostic species from stratigraphically coherent intervals thirteen radiolarian datum levels have been established defining ten zones and six subzones representing the lower to upper jurassic these zones are correlated with zones previously established by several workers for coeval strata of the world western tethys caucasus pacific coast of russia japan western pacific ocean and north america

radiolarian age constraints on mesotethyan ocean evolution and their implications for development of the bangong nujiang suture tibet radiolarian discoveries indicate that deep marine conditions prevailed in central tibet from the early middle jurassic until well into the early cretaceous late hauterivian early aptian 131 121 ma and help to constrain the temporal extent of oceanic conditions along the bangong nujiang suture these new fossils occur in chert or siliceous mudstone blocks associated with the lagkor tso ophiolitic melange basin inversion associated with closure of mesotethys between the qiangtang and lhasa terranes was accompanied by melange formation and predated regionally widespread deposition of overlying shallow marine late aptian albian orbitolinid limestones

seismic reflection evidence for a dangerous grounds miniplate no extrusion origin for the south china sea the collision of india and asia has caused large strike slip faults to form in east asia resulting in the extrusion of crustal blocks toward the southeast since the eocene as a result of the indentation of rigid india into asia it has been suggested that the south china sea opened as a result of relative motion between a rigid indochina sundaland block and china alternative models propose that rifting and seafloor spreading were driven by trench forces to the south we test these competing models by analysis of seismic reflection profiles across the boundary between sundaland and the southern rifted margin known as the dangerous grounds we show that the southern boundary of the dangerous grounds is a subduction zone that jammed in the middle miocene to the west the dangerous grounds are bounded by a strike slip zone also active until similar to 16 ma that becomes diffuse south of the now inactive south china sea seafloor spreading center we place the western edge of the dangerous grounds just to the east of the natuna arch lupar line the west baram line is confirmed as originating as a major strike slip fault within the dangerous grounds and is continuous with the red river fault zone because the dangerous grounds were independent of sundaland until similar to 6 ma its motion cannot have been constrained by motion of this block making extrusion impossible as a mechanism to rift the south china sea se motion by both the dangerous grounds and sundaland suggests subduction forces were the primary trigger for plate motions our reconstruction places a similar to 280 km upper limit on the motion on the red river fault and a similar to 1400 km width to the paleo south china sea

what are the spratly islands abstract seismic records combined with dredged samples and a core indicate that the spratly islands of the dangerous ground province are constructed of presently active carbonate build ups known to extend back continuously at least to the pleistocene and presumed to have initiated in the miocene most likely upon the crests of sea floor cuestas that trend north east south west parallel to the sea floor spreading magnetic anomalies of the contiguous abyssal plain of the southern part of the south china sea the cuestas range from spectacular to subdued constructed of triassic and cretaceous strata and no older rocks have been identified from dredges the cuesta axes plunge towards the south west away from the islands suggesting that the reefs began colonising their more elevated parts but the timing is uncertain the highest seismically recorded cuesta crest is in 440 m of water and the islands and reefs are generally closely surrounded by water deeper than 1500 m since the so called mid miocene unconformity mmu the region has been undergoing post rift thermal subsidence however the nearby seismic lines show no evidence of drowned carbonate reefs it is suggested that the coral algal reefs colonised the crests of the most elevated cuestas that have maintained stability as shown by the 165 m core of one reef indicating periodic exposure with caliche horizons deepening water has protected the build ups from extinction by post rift draping strata in contrast to the central luconia province and the build ups have been able to keep up with regional thermal subsidence the dredged mesozoic strata indicate that the dangerous ground is not exotic and should be interpreted as an integral part of the pre rift sundaland continent that included south china vietnam peninsular malaysia western sarawak and possibly part of sabah igneous and metamorphic samples have been dredged although individual spot k ar dates cannot be accepted at face value such rocks can also be interpreted as an integral part of sundaland post mmu dredged samples are predominantly deep water calcareous mudstones typified by the draping strata of the ocean drilling program odp site 1143 cored from recent to late miocene

precise radiolarian age constraints on the timing of ophiolite generation and sedimentation in the dazhuqu terrane yarlung tsangpo suture zone tibet well preserved abundant radiolarians provide high precision biostratigraphic age constraints on the timing of the eruption of ophiolitic basalts exposed along the yarlung tsangpo suture zone in southern tibet dazhuqu terrane ophiolites were generated in an intra oceanic supra subduction zone setting within a relatively short

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

the advection of mesoscale atmospheric vortices over reykjavik abstracton 12 august 2009 a series of satellite images revealed asymmetric shedding of atmospheric vortices in the lee of mt snaefellsjokull and their passage a distance of 120 km across faxafloi bay and over the city of reykjavik in west iceland after landfall the vortices were detected by a network of surface weather stations these observations are presented and with the aid of a numerical simulation they are discussed in view of existing theories of orographic wakes and vortex shedding in general the flow is in line with existing knowledge but there is a remarkable absence of vortices with anticyclonic rotation atmospheric conditions for vortices of this kind are most often favorable in late winter and spring and they are a forecasting challenge

palaeocene early eocene inversion of the phuquoc kampot som basin se asian deformation associated with the suturing of luconia abstract the little explored cambodian and vietnamese phuquoc kampot som basin is a late jurassic to early cretaceous foreland basin developed in response to the build up of a palaeo pacific magmatic arc a combination of seismic data well data and outcrop geology complemented by fission track and u pb analysis is used to unravel the basin history this reveals a hitherto unknown earliest palaeogene basin inversion associated with the luconian suturing to se asia and the shutdown of palaeo pacific subduction underneath se asia the phuquoc kampot som basin and the khorat basin in thailand constitute the erosional remnants of a larger basin that covered large parts of se asia in late mesozoic time and subsequently became segregated during earliest palaeogene inversion and erosion inversion was focused along the several hundred kilometres long kampot and khmer chanthaburi fold belts that confine the phuquoc kampot som basin and merge with the mae ping and the three pagodas fault zones these connections together with local nw se trending sinistral transpressional faults offshore indicate a link between initial se asian left lateral strike slip faulting and the luconian suturing the separation between the once unbroken khmer chanthaburi fold belt and the phetchabun fold belt in thailand suggests a 50 100 km cenozoic left lateral offset across the mae ping fault zone

oroclines and paleomagnetism in borneo and south east asia abstract oroclinal bending of borneo is interpreted to result from indentation and collision by the continental promontory of the miri zone central luconia province of northern sundaland into southern sundaland the collision caused strong compression and uplift of the intervening sibu zone upper cretaceous eocene rajang embaluh group turbidite basin that was floored by oceanic crust of the proto south china sea timing of the collision is indicated by uplift of turbidite formations to be overlain by upper eocene lower oligocene carbonates and intrusion of tin mineralised granites into the turbidites at the south east maximum inflexion of the orocline a region complicated by juxtaposition of both shallow and deep water formations the oroclinal model requiring clockwise rotation of the north west limb is given no support from the paleomagnetic data that instead demonstrate about 50 of cenozoic anti clockwise rotation unfortunately not a single outcrop of the strongly oroclinally bent sibu zone rocks was measured for paleomagnetism in the north west limb limited support was given for the required anti clockwise rotation in the north east limb previous syntheses emphasised anti clockwise rotation or stable non rotation of the greater borneo region as a coherent entity without any internal deformation such models have ignored the oroclinal shape defined by the areal geology of the island known since early dutch publications the northern thailand myanmar north south trending geology fabric results from indentation by a promontory of continental india at the assam yunnan oroclinal syntaxis resulting in paleomagnetically determined clockwise rotation the bend of peninsular malaysia and sumatra from north south changing to west east towards borneo in the south remains difficult to model because of widespread remagnetisation

mesozoic and cainozoic rocks dredged from the south china sea reed bank area and sulu sea and their significance for plate tectonic reconstructions abstract outcrops of pre quaternary rocks were sampled by dredging and coring during two cruises of rv sonne in the south china sea and sulu sea 1982 1983 late triassic deltaic sandstones wih plant remains are the oldest sediments recovered late jurassic early cretaceous regional metamorphism is indicated by gneiss and garnet mica schists exposed in the northwestern flanks of reed bank these rocks and occurrences of gabbro diorite dacite rhyolite and siliceous shale prove that the dangerous grounds and reed bank are underlain by a continental fragment during the period of seafloor spreading in the south china see a late oligocene to early miocene carbonate platform developed on this southwards drifting continental fragment which subsided in the middle miocene middle miocene andesite and early to middle miocene reefal carbonates were recovered from the cagayan ridge in the sulu sea the new data are in accord with the plate tectonic history developed by taylor and hayes 1980 1983 and holloway 1981

the mesoproterozoic maz terrane in the western sierras pampeanas argentina equivalent to the arequipa antofalla block of southern peru implications for west gondwana margin evolution the rocks of sierra de maz and sierra del espinal western sierras pampeanas represent pre famatinian ordovician basement isotope compositions nd and pb of metasedimentary rocks and shrimp u pb dating of detrital zircons combined with other geological evidence show that three parallel n s domains can be recognized the central maz domain contains pre grenvillian metasedimentary rocks deposited between 1 2 and 1 6 ga that underwent grenvillian granulite facies metamorphism and were intruded by mafic igneous rocks and massif type anorthosites metasedimentary rocks have high nd tdm ages 1 7 2 7 ga and very radiogenic pb 9 8 10 2 suggesting provenance from reworked early proterozoic or archean continental crust the domains to the east and west of the maz domain consist of three metasedimentary sequences with nd tdm ages between 1 2 and 1 6 ga and variably radiogenic pb 9 6 10 0 u pb shrimp dating of detrital zircons nd tdm model ages and comparison with other data suggest that these sequences are post grenvillian i e neoproterozoic and or early paleozoic the maz domain is interpreted as a suspect terrane similar to the northern arequipa antofalla craton that forms the basement of the central andes both underwent grenville age orogeny and were probably once continuous along the western margin of amazonia west gondwana

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

igneous petrogenesis of the yakuno ophiolite japan in the context of the diversity of ophiolites an ophiolite complex includes three major members basaltic volcanics mafic ultramafic cumulates and residual peridotite from the aspect of igneous petrology three distinct types are recognized among the associations of the three members liguria type alkalic basalt plagioclase type cumulates and lherzolite yakuno type high alumina tholeiite clinopyroxene type cumulates and clinopyroxene bearing harzburgite papua type low alumina tholeiite orthopyroxene type cumulates and clinopyroxene free harzburgite in the light of recent experimental studies the three types represent cogenetic complementary products of low 30 degrees of partial melting in the lherzolitic source mantle respectively the cumulates of the yakuno ophiolite show structural and chemical continuity to the underlying residual peridotite and were recrystallized at high pressures 5 10 kb they originated in a deep soft floored magma chamber directly overlying the partially melted residual harzburgite from which the magma was extracted the three members of the yakuno ophiolite were cogenetically formed through a magmatic event induced by a moderate degree of partial melting in the mantle

tectonic and paleobiogeographic significance of radiolarian microfaunas in the permian to mesozoic basement rocks of the north island new zealand abstract from the terranes sutured to the new zealand gondwana margin in mid cretaceous time the murihiku waipapa torlesse and mata river terranes have yielded tectonically and paleographically significant radiolarian faunas a late jurassic fauna from the murihiku forearc terrane is more cosmopolitan than coeval faunas from the waipapa faunas from the terranes east of the murihiku which all show evidence of accretion tectonics can be subdivided into ocean floor assemblages and assemblages of terrigenous clastic deposits waipapa ocean floor assemblages are typically tethyan while the terrigenous clastic assemblages are non tethyan possibly of southern hemisphere high latitude origin ocean floor assemblages show the same eastward younging trends opposed to the westward sedimentological younging due to imbrication as do the assemblages of the terrigenous clastics but are always a few tens of million years older radiolarians from ophiolites tangihua volcanics and matakaoa volcanics indicate that significant portions of the ocean floor obducted onto new zealand in late oligocene to earliest miocene time were of late cretaceous to early tertiary age

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

the structure of strongly stratified flow over hills dividing streamline concept in stably stratified flow over a three dimensional hill we can define a dividing streamline that separates those streamlines that pass around the hill from those that pass over the hill the height hs of this dividing streamline can be estimated by sheppard s simple energy argument fluid parcels originating far upstream of a hill at an elevation above hs have sufficient kinetic energy to rise over the top whereas those below hs must pass around the sides this prediction provides the basis for analysing an extensive range of laboratory observations and measurements of stably stratified flow over a variety of shapes and orientations of hills and with different upwind density and velocity profiles for symmetric hills and small upwind shear sheppard s expression provides a good estimate for hs for highly asymmetric flow and or in the presence of strong upwind shear the expression provides a lower limit for hs as the hills become more nearly two dimensional these experiments become less well defined because steady state conditions take progressively longer to be established the results of new studies are presented here of the development of the unsteady flow upwind of two dimensional hills in a finite length towing tank these measurements suggest that a very long tank would be required for steady state conditions to be established upstream of long ridges with or without small gaps and cast doubt upon the validity of previous laboratory studies

mesozoic tectonic evolution of the proto south china sea a perspective from radiolarian paleobiogeography abstract the proto south china sea pscs represents the lithosphere that formerly occupied the region southeast of south china where the present day south china sea is located the subduction and demise of the pscs have attracted wide attention whereas the pre subduction history particular the mesozoic of the region remains relatively neglected in this paper the radiolarian paleobiogeography of the region is analyzed to identify the paleobiogeographic affinity and paleo connectivity of the pscs with the pacific and tethys oceans during the mesozoic then the continent ocean configuration and tectonic evolution of the pscs and adjacent areas are discussed through the integration of paleobiogeographical results and associated paleomagnetic stratigraphic and petrologic data the main conclusions are as follows 1 during the triassic the pscs was situated in the transition zone between the pacific and tethys oceans and its paleobiogeography was influenced by both oceans the pscs was characterized by complex tectonic overprinting by the pacific and tethyan tectonic regimes 2 in the early middle jurassic the pscs was well connected to the pacific ocean but poorly connected to the tethys ocean consistent with the paleobiogeography of the pscs being mainly constrained by the pacific ocean the pscs was part of the paleo pacific slab 3 during the late jurassic cretaceous the pscs was in a semi closed environment the late jurassic early late cretaceous pscs was part of a west facing andean type subduction zone and the late late cretaceous pscs was situated in an extensional tectonic setting

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

radiolarian diversity patterns in the latest jurassic earliest cretaceous abstract the global diversity patterns of latest jurassic earliest cretaceous tithonian berriasian radiolarian faunas were analyzed based on samples from the european alps oman philippines and antarctica and an extensive literature survey several measures of diversity were applied to faunas from tropical oman mexico pacific subtropical alps california philippines japan and subpolar antarctic peninsula new zealand northern russia localities original diversity patterns are obscured by taxonomic sedimentological and preservational biases qualitative and quantitative corrections of these biases indicated a significant diversity gradient from tropical subtropical to subpolar latitudes but no significant difference between tropical and subtropical assemblages the latitudinal diversity gradient was apparently asymmetrical being steeper in the northern hemisphere than in the southern hemisphere in the southern hemisphere the diversity gradient was similar to the one observed in modern radiolarian sedimentary assemblages considering the more equable climate of the tithonian berriasian it appears unlikely that temperature was the only control of the observed diversity patterns the results substantiate the notion of latitudinal diversity gradients as a time invariant feature of the earth possibly driven by gradients in biome size

nd sr isotopes and elemental geochemistry of surface sediments from the south china sea implications for provenance tracing abstract the mineralogy major and trace elements and neodymium and strontium isotopes of surface sediments in the south china sea scs are documented with the aim of investigating their applicability in provenance tracing the results indicate that mineralogical compositions alone do not clearly identify the sources for the bulk sediments in the scs the nd isotopic compositions of the scs sediments show a clear zonal distribution the most negative end values were obtained for sediments from offshore south china 13 0 to 10 7 while those from offshore indochina are slightly more positive 10 7 to 9 4 the nd isotopic compositions of the sediments from offshore borneo are even higher with end ranging from 8 8 to 7 0 and the sediments offshore from the southern philippine arc have the most positive end values from 3 7 to 5 3 this zonal distribution in end is in good agreement with the nd isotopic compositions of the sediments supplied by river systems that drain into the corresponding regions indicating that nd isotopic compositions are an adequate proxy for provenance tracing of scs sediments sr isotopic compositions in contrast can only be used to identify the sediments from offshore south china and offshore from the southern philippine arc as the 87sr 86sr ratios of sediments from other regions overlapped similar zonal distributions are also apparent in a la th sc discrimination diagram sediments from the west margin of the scs such as those from beibuwan bay offshore from hainan island offshore from indochina and from the sunda shelf plot in the same field while those offshore from the northeastern scs offshore from borneo and offshore from the southern philippine arc plot in distinct fields thus the la th sc discrimination diagram coupled with nd isotopes can be used to trace the provenance of scs sediments using this method we re assessed the provenance changes of sediments at ocean drilling program odp site 1148 since the late oligocene the results indicate that sediments deposited after 23 8 ma above 455 mcd meters composite depth were supplied mainly from the eastern south china block with a negligible contribution from the interior of the south china block sediments deposited before 26 ma beneath 477 mcd were supplied mainly from the north palawan continental terrane which may retain the geochemical characteristics of the materials covered on the late mesozoic granitoids along the coastal south china for that the north palawan continental terrane is presently located within the southern philippine arc but was located close to odp site 1148 in the late oligocene the weathering products of volcanic material associated with the extension of the scs ocean crust also contributed to these sediments the rapid change in sediment source at 26 23 8 ma probably resulted from a sudden cessation of sediment supply from the north palawan continental terrane we suggest that the north palawan continental terrane drifted southwards along with the extension of the scs ocean crust during that time and when the basin was large enough the supply of sediment from the south to odp site 1148 at the north slope may have ceased

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

marginal basin evolution the southern south china sea abstract the southern south china sea is divided into contrasting morphology by the west baram line to the west is the sundaland extinct passive margin in which rifting began in the eocene 46 ma and ceased at 19 21 ma anomaly 6 where sea floor spreading began much later than along the shelf of china the break up hiatus lasted 3 5 ma marked by the mid miocene unconformity also preserved on land sarawak the post rift strata date from 16 ma and drape over the rifted topography to the east is a convergent margin that became a collision zone in the middle miocene the sunda shelf is of uniform 30 km thickness except in localised deep basins and extends to a water depth of 200 m the continental slope is narrow the continental rise dangerous grounds is covered by water ranging from 500 m to 3 5 km depth at the continent ocean transition its width ranges from 170 to 330 km the rajang delta extends over the shelf and continental slope its post rift sediments drape over the rifted proximal topography of the dangerous grounds to the east the drape is thinner and has not completely buried the rifted topography the cuestas appear to have supported the carbonate build up infrastructures of the spratly islands whose slopes rise abruptly from a sea floor of 2 3 km depth the sabah and brunei margin is a collision zone that was formerly convergent the on land geology indicates a mesozoic ophiolitic basement the main collision feature is the western cordillera constructed mainly of sandy eocene to lower miocene turbidites predominantly oligocene to lower miocene in the west crocker 32 18 ma uplifted episodically throughout the upper miocene and pliocene 14 8 ma the 2 km deep northwest borneo trough may be a relict of the convergence phase but could also be a collisional foredeep the oil prolific baram delta resulting from uplift and erosion of the western cordillera has built out as far as the northwest borneo trough it is suggested that the passive margin continental rise dangerous grounds has been underthrust beneath sabah to cause uplift of the western cordillera the west baram line accordingly abruptly separates the collision zone from the western extinct passive margin and is a now extinct major right lateral transform fault

early hettangian ammonites and radiolarians from the queen charlotte islands british columbia and their bearing on the definition of the triassic jurassic boundary abstract the triassic jurassic boundary t j boundary interval is one of the most important but poorly understood intervals in the phanerozoic here we fully document the ammonite and radiolarian successions at several sites in the queen charlotte islands qci british columbia eleven ammonite taxa are described and eighteen radiolarian taxa are discussed with the radiolarian genus tipperella described as new type species t kennecottensis n sp there are two continuous t j boundary sections in the qci one is located at kennecott point on graham island section i the other on the southeastern shore of kunga island section iii a second section at kennecott point contains fossils of early hettangian age only section ii radiolarian faunas include taxa from the upper rhaetian globolaxtorum tozeri zone in the two continuous sections and the lower hettangian canoptum merum zone in all three sections in each section the lowest hettangian fossils are radiolarians and a few collections contain rare rhaetian holdovers these mixed faunas may equate with the lowest hettangian ammonite zone the spelae zone of the north american succession the upper portion of section i contains a sparse ammonite fauna which indicates an early hettangian age this section has also provided carbon isotope data with a negative excursion spanning the t j boundary section ii contains a more diverse early hettangian ammonite assemblage that permits correlation of the upper portion of this section with the lower hettangian minutus zone section iii has been previously proposed as a potential basal hettangian global stratotype section and point gssp in addition to an outstanding radiolarian fauna the section contains moderately diverse early hettangian ammonites that permit correlation of the lower portion of the section with the minutus and pacificum zones and the upper portion with the lower hettangian polymorphum zone this section has previously provided a u pb date of 199 6 0 3 ma from 3 6 m below the t j boundary currently there are four candidates and no ideal gssp for the basal hettangian a section in new york canyon nevada has also been proposed as a potential gssp this section is easily accessible and provides a virtually complete ammonoid succession but lacks geochronology and microfossils the section on kunga island in the qci provides geochronologic data and excellent radiolarian constraints in essence the sections at kunga island in the qci and new york canyon in nevada are complementary close correlations between the two sections are possible using ammonite faunas we suggest the section from nevada be designated as holostratotype for the basal hettangian and the qci section be designated as a parastratotype to improve recognition of this interval

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

smithian and spathian early triassic ammonoid assemblages from terranes paleoceanographic and paleogeographic implications early triassic paleobiogeography is characterised by the stable supercontinental assembly of pangea however at that time several terranes such as the south kitakami massif sk south primorye sp and chulitna respectively and presently located in japan eastern russia and alaska straddled the vast oceans surrounding pangea by means of quantitative biogeographical methods including cluster analysis non metric multidimensional scaling and bootstrapped spanning network applied to smithian and spathian early triassic ammonoid assemblages we analyze similarity relationships between faunas and suggest paleopositions for the above cited terranes taxonomic similarities between faunas indicate that primary drivers of the ammonoid distribution were sea surface temperature and currents possible connections due to current controlled faunal exchanges between both sides of the panthalassa are shown and terranes such as sk sp and chulitna played an important role as stepping stones in the dispersal of ammonoids sk and sp terranes show strong sub equatorial affinities during the smithian thus suggesting a location close to south china at the same time the chulitna terrane shows strong affinities with equatorial faunas of the eastern panthalassa this paleoceanographic pattern was markedly altered during the spathian possibly indicating significant modifications of oceanic circulation at that time as illustrated by the development of a marked intertropical faunal belt across tethys and panthalassa

atmospheric karman vortex shedding from jeju island east china sea a numerical study abstracta mesoscale atmospheric numerical model is used to simulate two cases of karman vortex shedding in the lee of jeju island south korea in the winter of 2013 observed cloud patterns associated with the karman vortex shedding are successfully reproduced when the winter monsoon flows out from the eurasian continent a convective mixed layer develops through the supply of heat and moisture from the relatively warm yellow sea and encounters jeju island and dynamical conditions favorable for the formation of lee vortices are realized vortices that form behind the island induce updrafts to trigger cloud formation at the top of the convective boundary layer a sensitivity experiment in which surface drag on the island is eliminated demonstrates that the formation mechanism of the atmospheric karman vortex shedding is different from that behind a bluff body in classical fluid mechanics

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

a record of continental collision and regional sediment flux for the cretaceous and palaeogene core of se asia implications for early cenozoic palaeogeography abstract palaeogene sedimentary rocks exposed in west java were derived from local volcanic sources and central sundaland the continental core of se asia detrital zircons from seven sandstone samples contain u pb age populations with ages of 50 80 ma 74 145 ma 202 298 ma 480 653 ma and 723 1290 ma late cretaceous and palaeogene zircons in middle eocene forearc sandstones are interpreted as derived from two spatially and temporally discrete volcanic arcs located in java and sulawesi respectively in contrast all other populations have a sundaland provenance most permian triassic zircons were derived from granites of this age in the se asian tin belt mid cretaceous zircons in all upper eocene and lower oligocene formations were derived from the schwaner mountains of sw borneo the differences in zircon populations reflect changing sundaland sources with time in the middle eocene sediment was derived mainly from the tin belt from the late eocene onwards a borneo source became more important older zircon ages are from se asia basement that once formed part of gondwana zircons also record the timing of microcontinental collision at the java margin c 80 ma that halted cretaceous subduction and probably resulted in the elevation of large parts of continental se asia supplementary material methods sample locality list tables for u pb zircon age measurements point count data and heavy mineral assemblages sandstone petrographic descriptions and palaeocurrent data are available at www geolsoc org uk sup18489

paleomagnetic analysis of eastern tibet implications for the collisional and amalgamation history of the three rivers region sw china abstract a comparative analysis of paleolatitudes and latitudinal displacements was undertaken for the south china simao baoshan shan thai indochina qiangtang lhasa and himalayan blocks by using available paleomagnetic data to determine the collisional and amalgamation history of the main blocks in the three rivers region western yunnan the results show that 1 the simao block is a south china derived block 2 the baoshan and shan thai blocks were subjected to rapid northward drift during the period from late carboniferous to late permian 3 the baoshan block collided with the simao block in the late permian and continued to drift rapidly northwards together with the south china and shan thai blocks until the late triassic 4 the paleo tethys separating the baoshan and simao blocks was possibly opened in the early silurian 5 the meso tethys ranged in age from early permian time to early cretaceous time and reached its greatest width of about 42 latitude in the late triassic

the bentong raub suture zone abstract it is proposed that the bentong raub suture zone represents a segment of the main devonian to middle triassic palaeo tethys ocean and forms the boundary between the gondwana derived sibumasu and indochina terranes palaeo tethyan oceanic ribbon bedded cherts preserved in the suture zone range in age from middle devonian to middle permian and melange includes chert and limestone clasts that range in age from lower carboniferous to lower permian this indicates that the palaeo tethys opened in the devonian when indochina and other chinese blocks separated from gondwana and closed in the late triassic peninsular malaysia segment the suture zone is the result of northwards subduction of the palaeo tethys ocean beneath indochina in the late palaeozoic and the triassic collision of the sibumasu terrane with and the underthrusting of indochina tectonostratigraphic palaeobiogeographic and palaeomagnetic data indicate that the sibumasu terrane separated from gondwana in the late sakmarian and then drifted rapidly northwards during the permian triassic during the permian subduction phase the east malaya volcano plutonic arc with i type granitoids and intermediate to acidic volcanism was developed on the margin of indochina the main structural discontinuity in peninsular malaysia occurs between palaeozoic and triassic rocks and orogenic deformation appears to have been initiated in the upper permian to lower triassic when sibumasu began to collide with indochina during the early to middle triassic a type subduction and crustal thickening generated the main range syn to post orogenic granites which were emplaced in the late triassic early jurassic a foredeep basin developed on the depressed margin of sibumasu in front of the uplifted accretionary complex in which the semanggol formation rocks accumulated the suture zone is covered by a latest triassic jurassic and cretaceous mainly continental red bed overlap sequence

the jinshajiang ailaoshan suture zone china tectonostratigraphy age and evolution abstract the jinshajiang suture zone is important for enhancing our understanding of the evolution of the paleo tethys and its age tectonic setting and relationship to the ailaoshan suture zone have long been controversial based on integrated tectonic biostratigraphic chemostratigraphic and isotope geochronological studies four tectono stratigraphic units can be recognized in the jinshajiang suture zone the eaqing complex the jinshajiang ophiolitic melange the gajinxueshan group and the zhongxinrong group isotope geochronology indicates that the redefined eaqing complex composed of high grade metamorphic rocks might represent the metamorphic basement of the jinshajiang area or a remnant micro continental fragment eaqing complex protolith rocks are pre devonian and probably of early middle proterozoic age and are correlated with those of the ailaoshan complex two zircon u pb ages of 340 3 and 294 3 ma separately dated from the shusong and xuitui plagiogranites within the ophiolitic assemblage indicate that the jinshajiang oceanic lithosphere formed in latest devonian to earliest carboniferous times the oceanic lithosphere was formed in association with the opening and spreading of the jinshajiang oceanic basin and was contiguous and equivalent to the ailaoshan oceanic lithosphere preserved in the shuanggou ophiolitic melange in the ailaoshan suture zone the latter yielded a u pb age of 362 41 ma from plagiogranite the re defined gajinxueshan and zhongxinrong groups are dated as carboniferous to permian and latest permian to middle triassic respectively on the basis of fossils and u pb dating of basic volcanic interbeds the gajinxueshan group formed in bathyal slope to neritic shelf environments and the zhongxinrong group as bathyal to abyssal turbidites in the jinshajiang ailaoshan back arc basin latest permian earliest middle triassic synorogenic granitoids with ages of 238 18 and 227 5 255 8 ma respectively and an upper triassic overlap molasse sequence indicate a middle triassic age for the jinshajiang ailaoshan suture formed by collision of the changdu simao block with south china

late cretaceous to early tertiary structural elements of west kalimantan abstract recent geological and geophysical mapping in west kalimantan has allowed the definition of three domains with distinct geological and geophysical characteristics which were imprinted on the region by early cretaceous to eocene convergent tectonic events subduction related granitoids intruded low grade regional metamorphic rocks during the early cretaceous forming the schwaner mountains domain extending east west across the southern and central part of west kalimantan this is flanked in the northwest by a complex sequence of sedimentary and volcanic rocks ranging in age from late carboniferous to cretaceous which comprise the northwest kalimantan domain deformed cretaceous flysch deposits east of the northwest kalimantan domain form an accretionary complex representing the southern continuation of the extensive dominantly tertiary accretionary wedge in sarawak the boundary between the cretaceous accretionary domain and rocks of the northwest kalimantan domain is a fault which we interpret as a transform that marked the western limit of late cretaceous southward subduction beneath west kalimantan growth of the accretionary complex resulted in uplift of a ridge of melange and flysch deposits on which a half graben extensional basin formed and accumulated thick lacustrine deposits a sedimentary basin developed between continental rocks to the south and the emergent ridge comprising accretionary complex rocks and outer shelf deposits to the north in the position of a forearc basin as accretion proceeded the locus of underthrusting migrated northward and a second melange ridge and sedimentary basin developed farther to the north the evidence for accretionary processes and the association of these with sedimentary basin formation supports the hypothesis that an ancient south dipping subduction zone existed in the eastern part of west kalimantan during late cretaceous to early tertiary times

permian longitudes of wrangellia stikinia and eastern klamath terranes based on coral biogeography trend surface analysis of biogeographic data and probabilistic estimates of diversity and similarity provide a new approach to understanding the origin of north american suspect terranes results from permian corals indicate that 1 the eastern boundary of the tethyan coral province was about 2000 km west of the north american craton 2 eastern klamath and stikinia were close to one another and were up to 6700 km west of north america during the early permian 3 wrangellia was situated to the southeast of stikinia as much as 5000 km west of the craton 4 the late permian location of the eastern klamath terrane was 3000 5800 km west of the craton and between 11 and 21 n and 5 the eastern klamath terrane moved westward during the permian possibly as a result of back arc spreading

an observational study of vortex spacing in island wake vortex streets abstract vortex streets are a frequent occurrence in stratocumulus topped flow downwind of mountainous islands theoretical studies dating back to von karman supported by laboratory and numerical studies have yielded similarity theories for the size and spacing of these vortices behind bluff bodies despite dynamical differences between such two dimensional flows and the three dimensional flow past isolated islands satellite case studies suggest these geometric similarities may also hold for the atmospheric case in this study two of the resulting dimensionless ratios are measured using satellite imagery one is the aspect ratio between cross street and along street spacing of the vortices the second is the ratio of the cross street spacing to the crosswind width of the island a 30 image sample from the aqua and terra moderate resolution imaging spectroradiometer satellites is analyzed to obtain these ratios the resulting set of values for the two dimensionless ratios is tested against the values f

south china continental margin signature for sandstones and granites from palawan philippines abstract we report results of heavy mineral analysis and u pb dating of detrital zircons from metasediments and cenozoic sandstones and u pb dating of zircons from cenozoic granites of the north palawan continental terrane npct and the south palawan terrane spt the npct metasediments are derived mainly from granitic and metamorphic rocks of continental character they contain zircons that indicate a maximum depositional age of late cretaceous and other age populations indicating a south china origin the sediments were deposited on the south china margin before rifting of the continental margin during opening of the south china sea miocene spt sandstones contain similar heavy mineral assemblages suggesting sources that included npct metasediments metamorphic basement rocks at the contact between the spt and the npct south china sea rift volcanic and or minor intrusive rocks and the palawan ophiolite complex the spt sandstones are very similar to lower miocene kudat formation sandstones of northern borneo suggesting a short lived episode of sediment transport from palawan to borneo in the early miocene following arc continent collision u pb dating of zircons shows that the central palawan granite is eocene 42 0 5 ma the capoas granite was intruded during a single pulse or as two separate pulses between 13 8 0 2 ma and 13 5 0 2 ma inherited zircon ages from the capoas granite imply melting of continental crust derived from the south china margin with a contribution from cenozoic rift related and arc material

contraction and extension in northern borneo driven by subduction rollback abstract during the paleogene the proto south china sea was subducted beneath northern borneo subduction ended with early miocene collision of the dangerous grounds reed bank north palawan block and the sabah cagayan arc much of northern borneo then became emergent forming the top crocker unconformity later in the early miocene subsidence resumed it is proposed that northward subduction of the celebes sea initiated formation of the sulu sea backarc basin followed by subduction rollback to the se this formed a volcanic arc which emerged briefly above sea level and collapsed in the middle miocene as rollback continued the sulu arc was active during middle and late miocene between sabah and the philippines rollback drove extension in northern borneo and palawan accompanied by elevation of mountains crustal melting and deformation offshore there were two important extensional episodes the first at about 16 ma is marked by the deep regional unconformity and the second at about 10 ma produced the shallow regional unconformity both episodes caused exhumation of deep crust probably on low angle detachments and were followed by granite magmatism the nw borneo palawan trough and offshore sabah fold and thrust belt are often interpreted as features resulting from collision regional compression or subduction however there is no seismicity dipping slab or volcanicity indicating subduction nor obvious causes of compression the trough developed after the middle miocene and is not the position of the paleogene trench nor the site of neogene subduction inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough the trough is interpreted as a flexural response to gravity driven deformation of the sediment wedge caused by uplift on land that resulted from extension with a contribution of deep crustal flow

tectonic characteristics and evolution history of the pearl river mouth basin abstract on the basis of the new understandings from tens of thousand of kilometres of geophysical material and over 60 exploration and evaluation wells providing data on the pearl river mouth basin prmb this paper analyses the special tectonic position of the prmb where three major plates i e the eurasian the pacific and the indo australian plates meet and interact the characteristics of the basin geological structure and its tectonic evolution are also discussed situated on continental and transitional crust the prmb is a mesozoic cenozoic oil and gas bearing basin developed on caledonian folding basement which was reformed during the mesozoic in the process of its formation and evolution the prmb underwent extension slight compression and re extension with the eruption of intermediate acid and basic magma meanwhile it formed double structural layers with faulting below and depression above and sediments were laid down with marine facies following continental facies hydrocarbons accumulated from continental source rocks in the marine reservoir rocks by using a fracture structure model of the uplift and depression the mechanism of the prmb and its evolution history have been interpreted

paleogeography of jurassic fragments in the caribbean jurassic rocks of the caribbean are a sampling of 100 million years of farallon plate history with fragments originating at diverse paleolatitudes and from varied tectonic settings fragments with clear paleogeographic signatures are components of the basement complexes of duarte in hispaniola bermeja in puerto rico and la desirade off guadeloupe paleolatitudinally sensitive radiolarian faunas document origination of duarte as equatorial la desirade as higher latitude and various bermeja cherts as both equatorial and higher latitude red ribbon chert of duarte and bermeja of the same age physical appearance and lithological association are probably dismembered components of the same slab of pacific crust la desirade red ribbon chert is slightly younger than the duarte and bermeja red ribbon chert and was deposited at higher latitude bermeja tuffaceous chert is also of higher latitude and probably had an arc proximal origin on the basis of modeled plate trajectories in the pacific the origin of various cherts from different paleolatitudes that end up in the same location requires different arrival times at the trench between north and south america based on radiolarian paleobiogeography plus indications of origin at a spreading ridge and ignoring the poorly constrained modeled trajectories for the late jurassic at least one of the higher latitude fragments may have originated in the southern hemisphere the accumulation of multifarious chert greenstone and other ocean floor components was accomplished by offscraping strata transported to the subduction zone along the eastern pacific margin and warehousing this material in an accretionary complex prior to entry of the caribbean plate into the gap between north and south america

middle to late cenozoic tectonic events in south and central palawan philippines and their implications to the evolution of the south eastern margin of south china sea evidence from onshore structural and offshore seismic data abstract using recently gathered onland structural and 2d 3d offshore seismic data in south and central palawan philippines this paper presents a new perspective in unraveling the cenozoic tectonic history of the southeastern margin of the south china sea south and central palawan are dominated by mesozoic ophiolites palawan ophiolite distinct from the primarily continental composition of the north these ophiolites are emplaced over syn rift eocene turbidites panas formation along thrust structures best preserved in the ophiolite turbidite contact as well as within the ophiolites thrusting is sealed by early miocene 20 ma sediments of the pagasa formation isugod formation onland constraining the younger limit of ophiolite emplacement at end late oligocene 23 ma the onset of ophiolite emplacement at end eocene is constrained by thrust related metamorphism of the eocene turbidites and post emplacement underthrusting of late oligocene early miocene nido limestone this carbonate underthrusting at end early miocene 16 ma is marked by the deformation of a seismic unit corresponding to the earliest members of the early middle miocene pagasa formation within this formation a tectonic wedge was built within middle miocene from 16 ma to 12 ma forming a thrust fold belt called the pagasa wedge wedge deformation is truncated by the regionally observed middle miocene unconformity mmu 12 ma a localized post kinematic extension affects thrust fold structures the mmu and late miocene to early pliocene carbonates e g tabon limestone this structural set up suggests a continuous convergent regime affecting the southeastern margin of the south china sea between end eocene to end middle miocene the ensuing structures including juxtaposed carbonates turbidites and shallow marine clastics within thrust fold belts have become ideal environments for hydrocarbon generation and accumulation best developed in the northwest borneo trough area the intensity of thrust fold deformation decreases towards the northeast into offshore southwest palawan

the radiolarian evidence for the accretion of the fu saki formation with the inferred oceanic plate stratigraphy a case of weakly metamorphosed accretionary complex in ishigaki jima southern ryukyu arc japan abstract the island of ishigaki jima located in the western part of the southern ryukyu arc japan is underlain by a basement comprising the tumuru and fu saki formations the former is a pelitic glaucophane schist with a metamorphic age of 220 190 ma and the latter is a weakly metamorphosed accretionary complex composed mainly of chert mudstone and sandstone with minor amounts of limestone and mafic rocks the fu saki formation was weakly metamorphosed at 140 ma latest carboniferous early jurassic microfossils have been obtained from the limestones cherts and siliceous mudstones of this formation but no fossils have been collected from the phyllitic mudstones the radiolarian fauna of the phyllitic mudstones described herein indicates a late pliensbachian early toarcian early jurassic age this result when combined with existing data enables the reconstruction of an oceanic plate stratigraphy showing a succession of in ascending order upper carboniferous triassic cherts sinemurian lower pliensbachian siliceous mudstones and upper pliensbachian lower toarcian phyllitic mudstones and sandstones the radiolarians from the phyllitic mudstones are important in constraining the timing of the accretion of the fu saki formation to the base of the tumuru formation

jurassic cretaceous radiolarian biostratigraphy and sedimentary environments of the ceno tethys records from the xialu chert in the yarlung zangbo suture zone southern tibet radiolarian biostratigraphic research has been carried out along two continuous sections through the xialu chert one of the accreted sheets included in the yarlung zangbo suture zone six radiolarian zones have been identified as follows laxtorum jurassicum zone aalenian tricolocapsa plicarum zone bajocian lower bathonian stylocapsa spiralis zone upper callovian oxfordian hsuum maxwelli zone kimmeridgian pseudodictyomitra carpatica zone upper tithonian lower valanginian and turbocapsula costata zone aptian a reconstructed stratigraphy of the xialu chert based on lithological succession and radiolarian dating indicates that the chert exhibits a long depositional history at least from early middle jurassic aalenian to late early cretaceous aptian the separation of the lhasa block from the northern gondwana margin must therefore be dated before the aalenian the absence of calcareous sediments in the xialu chert indicates that the oceanic basin was deeper than the ccd throughout the depositional history the transition from chert to siliceous mudstone is recorded sometime in early cretaceous most probably around the barremian aptian boundary this means that the oceanic plate had already started being consumed at a trench by that time the accretion of the xialu chert occurred after the aptian time

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

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

granitic magmatism basement ages and provenance indicators in the malay peninsula insights from detrital zircon u pb and hf isotope data abstract the malay peninsula lies on two continental blocks sibumasu and east malaya which are intruded by granitoids in two provinces the main range and eastern previous models propose that permian triassic granitoids are subduction related and syn to post collisional we present 752 u pb analyses that were carried out on zircons from river sands in the malay peninsula of these 243 grains were selected for hf isotope analyses our data suggest a more complex sibumasu east malaya collision history 176hf 177hfi ratios reveal that permian triassic zircons were sourced from three magmatic suites a permian crustally derived granitoids b early middle triassic granitoids with mixed mantle crust sources and c late triassic crustally derived granitoids this suggests three permian triassic episodes of magmatism in the malay peninsula two of which occurred in the eastern province although the exact timing of the sibumasu east malaya collision remains unresolved current data suggest that it occurred before the late triassic probably in late permian early triassic our data also indicate that sibumasu and east malaya basements are chronologically heterogeneous but predominantly of proterozoic age some basement may be neoarchaean but there is no evidence for basement older than 2 8 ga finally we show that hf isotope signatures of triassic zircons can be used as provenance indicators

gondwana and cathaysian blocks palaeotethys sutures and cenozoic tectonics in south east asia the triassic indosinian orogeny followed extinction of the palaeotethys ocean resulting in suturing of gondwana affinity and cathaysian blocks

cretaceous accretionary collision complexes in central indonesia abstract the geology of cretaceous accretionary collision complexes in central indonesia is reviewed in this paper the author and his colleagues have investigated the cretaceous accretionary collision complexes by means of radiolarian biostratigraphy and metamorphic petrology as well as by geological mapping the results of their work has revealed aspects of the tectonic development of the sundaland margin in cretaceous time the cretaceous accretionary collision complexes are composed of various tectonic units formed by accretionary or collision processes forearc sedimentation arc volcanism and back arc spreading the tectonic units consist of chert limestone basalt siliceous shale sandstone shale volcanic breccia conglomerate high p t and ultra high p metamorphic rocks and ultramafic rocks dismembered ophiolite all these components were accreted along the cretaceous convergent margin of the sundaland craton in the cretaceous the southeastern margin of sundaland was surrounded by a marginal sea an immature volcanic arc was developed peripherally to this marginal sea an oceanic plate was being subducted beneath the volcanic arc from the south the oceanic plate carried microcontinents which were detached fragments of gondwanaland oceanic plate subduction caused arc volcanism and formed an accretionary wedge the accretionary wedge included fragments of oceanic crust such as chert siliceous shale limestone and pillow basalt a jurassic shallow marine allochthonous formation was emplaced by the collision of continental blocks this collision also exhumed very high and ultra high pressure metamorphic rocks from the deeper part of the pre existing accretionary wedge cretaceous tectonic units were rearranged by thrusting and lateral faulting in the cenozoic era when successive collision of continental blocks and rotation of continental blocks occurred in the indonesian region