asymmetry of atmospheric circulation anomalies over the western north pacific between el nino and la nina the asymmetry of the western north pacific wnp low level atmospheric circulation anomalies between the el nino and la nina mature winter is examined an anomalous wnp cyclone wnpc center during la nina tends to shift westward relative to an anomalous wnp anticyclone wnpac center during el nino two factors may contribute to this asymmetric response thefirst factor is the longitudinal shifting of el nino and la nina anomalous heating the composite negative precipitation anomaly center during la ninai s located farther to the west of the composite positive precipitation anomaly center during el nino the westward shift of the heating may further push the wnpc westward relative to the position of the wnpac the second factor is the amplitude asymmetry of sea surface temperature anomalies sstas in the wnp namely the amplitude of local cold ssta during el nino is greater than that of warm ssta during la nina the asymmetry of ssta is originated from the asymmetric ssta tendencies during the enso developing summer although both precipitation and surface wind anomalies are approximately symmetric the surface latent heat flux anomalies are highly asymmetric over the key wnp region where the climate mean zonal wind speed is small both the anomalous westerly during el nino and the anomalous easterly during la nina in the region lead to an enhanced surface evaporation strengthening weakening the enhancement of the cold warm ssta in situ during el nino la nina the asymmetry of the ssta in the wnp is further amplified due to anomalous wind differences between el nino and la nina in their mature winter atmo spheric general circulation model experiments demonstrate that both factors contribute to the asymmetry between the wnpac and wnpc the asymmetric circulation in the wnp contributes to the asymmetry of temporal evolutions between el nino and la nina

asymmetry of the indian ocean basinwide sst anomalies roles of enso and iod abstract a basinwide warming cooling in the indian ocean is observed following the el nino la nina mature phase with the amplitude of the warming being significantly larger than the cooling a composite analysis reveals that the amplitude asymmetry positive skewness between the warm and cold indian ocean basinwide sea surface temperature anomaly pattern iob appears only when enso is concurrent with the indian ocean dipole iod the amplitude asymmetry becomes insignificant during the enso only and the iod only events the physical mechanism for the amplitude asymmetry is investigated by analyzing the mixed layer heat budget based on the simple ocean data assimilation soda 2 0 2 data it is found that the positive skewness in the iod west pole iodw is mainly caused by the asymmetry of ocean temperature advection whereas the positive skewness in the iod east pole iode is caused by the asymmetry of the surface heat flux anomaly primarily shortwave radiation in response to the enso remote f

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

a new discovery of glossopteris in southeastern mongolia as an argument for distant migration of gondwanan plants abstract well preserved leaves conforming to the fossil genus glossopteris are found in the permian deposits of southeastern gobi khatan bulag locality mongolia these leaves have many features in common with glossopteris communis feistmantel described from india the locality khatan bulag belongs to sulinkheer nappe fold tectonic megazone the glossopteris sp cf g communis specimens from the khatan bulag suggest that there was effective migration gateway between gondwana and southern regions of asia in the mid permian

using palaeomagnetism to determine late mesoproterozoic palaeogeographic history and tectonic relations of the sinclair terrane namaqua orogen namibia

acquisition of chemical remanent magnetization during experimental ferrihydrite hematite conversion in earth like magnetic field implications for paleomagnetic studies of red beds abstract hematite bearing red beds are renowned for their chemical remanent magnetization crm if the crm was acquired substantially later than the sediment was formed this severely compromises paleomagnetic records to improve our interpretation of the natural remanent magnetization the intricacies of the crm acquisition process must be understood here we contribute to this issue by synthesizing hematite under controlled earth like field conditions 100 t crm was imparted in 90 oriented samples with varying inclinations the final synthesis product appeared to be dominated by hematite with traces of ferrimagnetic iron oxides when the magnetic field intensity is 40 t the crm records the field direction faithfully however for field intensities 40 t the crm direction may deviate considerably from that of the applied field during synthesis the crm intensity normalized by the isothermal remanent magnetization crm irm 2 5 t increases linearly with the intensity of growth field implying that crm could potentially be useful for relative paleointensity studies if hematite particles of chemical origins have consistent properties crm in hematite has a distributed unblocking temperature spectrum from 200 to 650 c while hematite with a depositional remanent magnetization drm has a more confined spectrum from 600 to 680 c because it is usually coarser grained and more stoichiometric therefore the thermal decay curves of crm with their concave shape are notably different from their drm counterparts which are convex these differences together are suggested to be a potential discriminator of crm from drm carried by hematite in natural red beds and of significance for the interpretation of paleomagnetic studies on red beds

apparent polar wander paths of the major chinese blocks since the late paleozoic toward restoring the amalgamation history of east eurasia abstract high quality paleomagnetic poles a k a paleopoles are essential for quantitative lithospheric plate reconstruction however the current paleomagnetic database of the major chinese blocks including the north china block ncb the south china block scb and the tarim block tb since the late paleozoic era contain outdated and low quality data here we update the database by adding recently published high quality paleopoles and rejecting low quality outdated ones the database includes 288 paleopoles published 1980 2014 90 of them published after 2000 following the van der voo selection criteria 75 paleopoles each with a quality factor q smaller than 4 were rejected in the first round of selection we then removed another 59 paleopoles that have been locally rotated or shallowed since the acquisition of stable remanence eventually 154 paleopoles were selected and adopted to calculate the new apparent polar wander paths apwps for the major chinese blocks we found comparable clastic and igneous paleopoles at intervals when a quantitative comparison was available as such comparison was not possible during most periods epochs our conclusions reflect an unclear extent of inclination errors in chinese clastic paleopoles new models of the chinese apwps with and without inclination error corrections were computed from carefully selected paleopoles version 1 running mean v1rm paths were calculated at the period epoch level version 2 running mean v2rm paths were computed in a set sliding time window of 20 or 30 myr spline paths were calculated with the same time windows along with a smoothing parameter of 50 using a recent global reconstruction model and up to date geological observations new models of the chinese apwps allowed us to re evaluate the coalescence history of east eurasia since the late paleozoic era four major tectonic events were confirmed 1 the tb accreted with the kazakhstan orocline during amalgamation of the west altaids during the middle late permian period ca 265 250 ma 2 the suturing of the ncb and the scb likely occurred in a scissor like pattern and had been accomplished no later than the middle jurassic period ca 180 160 ma 3 the amalgamation between the ncb and the tb along with the microblocks between the two might have been achieved during the late jurassic early cretaceous periods ca 160 140 ma 4 the mongol okhotsk ocean should have been closed no later than the early cretaceous period ca 140 120 ma

different impacts of various el nino events on the indian ocean dipole our early work wang and wang in j clim 26 1322 1338 2013 separates el nino modoki events into el nino modoki i and ii because they show different impacts on rainfall in southern china and typhoon landfall activity the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively el nino modoki i features a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modoki ii shows an asymmetric distribution with the warm sst anomalies extending from the northeastern pacific to the equatorial central pacific the present paper investigates the influence of the various groups of el nino events on the indian ocean dipole iod similar to canonical el nino el nino modoki i is associated with a weakening of the walker circulation in the indo pacific region which decreases precipitation in the eastern tropical indian ocean and maritime continent and thus results in the surface easterly wind anomalies off java sumatra under the bjerknes feedback the easterly wind anomalies induce cold sst anomalies off java sumatra and thus a positive iod tends to occur in the indian ocean during canonical el nino and el nino modoki i however el nino modoki ii has an opposite impact on the walker circulation resulting in more precipitation and surface westerly wind anomalies off java sumatra thus el nino modoki ii is favorable for the onset and development of a negative iod on the frame of the bjerknes feedback

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

different sources involved in generation of continental arc volcanism the carboniferous permian volcanic rocks in the northern margin of the north china block abstract new zircon u pb dating results on the carboniferous permian volcanic rocks in the northern margin of the north china block ncb indicate their eruption during the early carboniferous to late permian from 347 3 ma to 258 1 ma and a slight decrease of the upper limits of the volcanic sequences from west to east they have a main rock association of basalt basaltic andesite andesite dacite rhyolite tuff and tufaceous sandstone most of them have calc alkaline compositions and exhibit variable sio2 contents from 48 2 wt to 77 1 wt there is no significant gap between the mafic and felsic volcanic rocks in major and trace element classification diagrams indicating that they are not bimodal in composition the carboniferous permian volcanic rocks exhibit subduction related geochemical features such as negative nb and ta anomalies of mafic to intermediate rocks on primitive mantle normalized diagrams indicating they were formed in an andean type continental arc during southward subduction of the paleo asian oceanic plate beneath the northern ncb however their wide range of whole rock sr nd and zircon hf isotopic compositions indicate that their source areas are very complex and different sources were involved in generation of these volcanic rocks geochemical and sr nd hf isotopic results show that the basalt and some andesite were produced by fractional crystallization of mafic magma derived from partial melting of mantle wedge and subducted oceanic crust however most of the intermediate to felsic volcanic rocks were derived from partial melting of lower continental crust there is an increasing input of crustal materials from the carboniferous to permian as indicated by increasing volumes of felsic volcanic rocks in the volcanic sequences the results show that origin of the continental arc volcanism is very complex and both materials from the subducted oceanic crust and sediments mantle wedge and arc continental crust could be involved in their generation for the permian andesite dacite and rhyolitic volcanic rocks there is a striking correlation between their sr nd hf isotopic compositions and those of the underlying basement sr nd hf isotopic differences between the permian intermediate to felsic volcanic rocks from either side of the northern boundary fault of the north china craton suggest that mixture and homogenization of the magmas in the melting assimilation storage hybridization mash zone within this continental arc was incomplete and incomplete homogenization of magmas is likely a common feature of many mash zones within continental arcs our results on the volcanic rocks also show that the final closure of the paleo asian ocean along the solonker suture zone has not been finished prior to the middle permian and the decease of the paleo asian oceanic subduction beneath the northern ncb in its middle western parts is a little earlier than that in its eastern part

new paleomagnetic results from the lhasa block revised estimation of latitudinal shortening across tibet and implications for dating the india asia collision knowing how and when the tibetan plateau formed is of global concern as high topography modifies climate circulation patterns and alters species migration paths previous paleomagnetic work suggested that intracontinental shortening from deformation related to the india asia collision played a major role in building the tibetan plateau however these studies were derived from red bed facies which are often afflicted by inclination shallowing leading to overestimates of continental shortening we report new paleomagnetic data from the lhasa block the southern continental margin of asia before the india asia collision a high temperature characteristic remanent magnetization chrm was isolated from 43 sites of late cretaceous red beds 32 sites of late cretaceous lava flows and nine sites of eocene tuffs all the chrm directions are significantly different from the present day geomagnetic field and the mean directions of red beds lava flows and tuffs pass the fold test the distribution patterns of chrm directions derived from volcanic rocks are consistent with a secular variation model suggesting that secular variation was likely averaged out in contrast the red bed chrm directions exhibit an east west elongated distribution pattern indicative of inclination flattening the mean chrm inclination of the red beds 23 5 degrees 2 5 degrees is consistent with previous results but significantly shallower than that of 41 9 degrees 4 4 degrees carried by the coeval lava flows an elongation inclination analysis of the red bed chrm directions yielded an unflattened mean inclination of 39 7 degrees with 95 confidence limits between 37 7 degrees and 41 9 degrees the paleolatitudes of the late cretaceous volcanic rocks and inclination corrected sediments suggest about 10 degrees less shortening occurred between lhasa and siberia than previous estimates with total shortening lying between 3 3 degrees 2 6 degrees and 7 3 degrees 5 4 degrees since the late cretaceous the mean chrm inclination derived from the eocene tuffs 51 8 degrees 5 2 degrees is indistinguishable from the expected reference direction our new results imply that india asia convergence was accommodated mainly through consumption of the india plate and yield a much younger age ca 43 ma for the initial india asia collision than previously estimated by paleomagnetic data c 2010 elsevier b v all rights reserved

tectonic evolution of the tancheng lujiang tan lu fault via middle triassic to early cenozoic paleomagnetic data the north striking tancheng lujiang tan lu fault is a conspicuous and controversial feature of the eastern asian landscape near the southeast extremity of the fault in anhui province we collected paleomagnetic samples at 17 middle triassic t2 and 10 upper cretaceous k2 to lower cenozoic e1 sites t2 remanent magnetizations are interpreted as primary in two of three areas the three areas are rotated 37 to 137 counterclockwise with respect to the south china block scb reference direction k2 e1 remanent magnetization directions pass regional fold and reversals tests and are not rotated with respect to surrounding areas counterclockwise rotation of t2 strata therefore ended before k2 and is attributed to left lateral shear acting along tan lu during the north china block ncb scb collision in shandong province 700 km north of the anhui sites four areas containing 33 upper jurassic j3 and cretaceous sites have negligible declination differences except for one which has dispersed directions the fold test is inconclusive for this latter area and positive for the other three regional concordance of the j3 e1 paleomagnetic data including paleolatitudes together with observed deformation patterns suggest that an extensional regime prevailed in the late cretaceous and cenozoic euler pole positions that constrain the north south china collision and account for tan lu motion suggest at least 500 km of sinistral shear took place along the fault and either 1 subduction and related ultrahigh pressure uhp metamorphism occurred near the present location of the qinling dabieshan and sulu uhp belts while tan lu acted as a transform fault that connected the two subduction zones or 2 tan lu and sulu were parts of the same transform fault system and no uhp rocks formed in situ at sulu in either case uhp rocks originally exhumed near dabieshan could have been transported by plate capture toward sulu along tan lu after north and south china impacted near dabieshan the tan lu fault grew within the scb as the dabieshan corner indented the scb causing folds in scb cover rocks to conform to the ncb margin late cretaceous to cenozoic reactivation of tan lu with both right lateral strike slip and normal fault motion occurred as the scb extruded east relative to the ncb under the influence of the india asia collision

crustal structures revealed from a deep seismic reflection profile across the solonker suture zone of the central asian orogenic belt northern china an integrated interpretation abstract the solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the central asian orogenic belt caob an 630 km long reflection seismic profile across this suture was recently completed by the chinese sinoprobe project the processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models the moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of 40 45 km 14 5 s two way travel time which is in agreement with the refraction data recorded along the same profile in a broad view the profile images an orogen that appears bivergent with and approximately centered on the solonker suture zone the southern portion of this profile is dominated by a crustal scale cratonward propagating fold and thrust system that formed during the late permian and triassic through collision and subsequent convergence in a post collisional stage the major thrust faults are truncated by mesozoic granitoid plutons in the upper crust and by the moho at the base of the crust this geometry suggests that the moho was formed after the thrusting event the northern portion of the profile although partially obliterated by post collisional magmatic bodies shows major south dipping folding and thrusting bands of layered reflectors immediately overlying the moho are interpreted as basaltic sills derived from the mantle episodic mafic underplating may have occurred in this region giving rise to post collisional magmatic events and renewal of the moho a few mantle reflectors are also visible the overall geometry of these mantle reflectors supports the tectonic models that the southern orogen manchurides experienced south directed subduction and the northern orogen altaids underwent north directed subduction prior to collision along the solonker suture zone

triassic southeastward subduction of north china block to south china block insights from new geological geophysical and geochemical data abstract lithospheric subduction prior to the assembly of the south china and north china blocks is traditionally considered to be directed northward however some critical geological and geochemical data cannot be reconciled with this northward subduction this paper presents new lines of evidence against the traditional models and proposes a new and revolutionary tectonic model to explain the distribution and exhumation of high pressure hp ultrahigh pressure uhp metamorphic rocks of the dabie sulu belt we emphasize the following 1 the triassic tectonic environment of the southern margin of the north china block was passive not active based on the stratigraphy 2 in the southern margin of the north china block no arc magmatism was recorded 3 many paleoproterozoic slices of jiaobei affinity of the jiao liao ji belt in the north china block were located in the triassic sulu orogen 4 many 1 85 ga metamorphic zircons are preserved in the dabie sulu high pressure ultra high pressure hp uhp metamorphic rocks 5 the geometric asymmetry of many structural patterns in the hp uhp slices indicates top to the northwest thrusting during the exhumation of hp uhp slices 6 blueschists occur in the south of the uhp eclogite slices 7 in the eastern segment of the north qinling orogen no components with an affinity of the south china block have been found along the shangdan suture of the qinling orogen has been recorded an apparent northward subduction we consider that the suture is just a lateral subduction zone rather than a major collisional zone along the shangdan suture the rarity of i type plutonism can be attributed to a transform type continental margin the bureya jiamusi khanka block has an affinity to the south china block based on its similarity regarding the paleozoic history of deformation and triassic blueschist metamorphic facies metamorphism the bureya jiamusi khanka block could be the northern extension of the dabie sulu belt and this gigantic belt could be interpreted as an orocline related to the southeastward subduction of the north china block beneath the greater south china block

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

role of the enso indian ocean coupling on enso variability in a coupled gcm warming are only confined to the io and it has little impact on the tropical pacific during the boreal winter when the el nino is in its mature phase the anomalous warming extends eastward to cover the entire tropical io and the anomalous easterlies extend into the western pacific wp the anom alous easterlies in the wp generate oceanic upwelling kelvin waves which propagate eastward and accelerate the decay of the warm sst in the eastern pacific as a result the el nino is rapidly terminated and a la nina develops within one year from the el nino mature phase they concluded that the interaction between enso and the io may generate a biennial tendency for enso 4 the samples used for the composite analysis by kk06 are rather limited due to the relatively short length of the observational data in this study we intended to analyze a longer 200 yr data set obtained from the simulation of a sintex f scale interaction experiment frcgc cou pled gcm in order to verify the enso io feedback hypoth esis itturnsoutthatthefeedbackprocessbetweenensoand the io is quite plausible not only from observations but also from the state of the art coupled gcm

solonker suture in east asia and its bearing on the final closure of the eastern segment of the palaeo asian ocean abstract the location and tectonic nature of the solonker suture in east asia and hence the late palaeozoic to early mesozoic closure of the palaeo asian ocean have notoriously been enigmatic in the past decades due to limited rock exposure and the absence of unambiguous collision related regional features several tectonic models have been proposed since but in many cases these models were derived only from single key exposures or methodologies often being over simplified or interpreted leading to questionable extrapolations on regional and global scales despite the complexity of the palaeozoic accretionary tectonic framework now the regionally consistent availability of geochronological geochemical stratigraphic and palaeo geographic data enables us to integrate these into a highly detailed and coherent palaeozoic tectonic review of the suture the region across the solonker suture can generally be subdivided into three major palaeozoic tectonic provinces e g i a sino cratonic province that resembles the active palaeozoic northern margin of the north china craton to the south of the suture ii a mongolian province that comprises the south eastern margin of the mongolian terrane to the north of the suture and iii an east asian pre pacific province in north east china that accreted with the late permian initiation of pacific plate subduction the sino cratonic province experienced episodic tectonic activity that includes the accretion of the initially ensialic bainaimiao arc onto the passive northern margin of the north china craton at 437 453 ma subsequent southward directed subduction activity beneath the amalgamated margin until at least 400 ma followed by a temporary cessation of magmatic activity accompanied by a switch from north to southward directed continental drift and finally concluded by renewed subduction activity until the final closure of the palaeo asian ocean the mongolian province is suggested to have been more closely associated with the siberian craton before the presumably late devonian opening of the mongol okhotsk ocean the east asian pre pacific province originally rifted away from the eastern margin of gondwana at 600 750 ma recorded early palaeozoic 500 ma orogenic processes along the then northern margin of the siberian craton the baolidao arc system successively developed along the present day south eastern margin of the mongolian province due to continued subduction activity throughout the palaeozoic after the middle carboniferous opening of the hegenshan back arc basin renewed subduction beneath a matured baolidao arc during carboniferous and permian times led to the obduction of the hegenshan ophiolite not earlier than 270 ma shortly after the palaeo asian ocean diachronously closed from west to east along the solonker suture in the late permian to early triassic the east asian pre pacific province re attached itself by the mid mesozoic followed by a change in the regional stress regime controlled by palaeo pacific plate subduction a divergent double sided subduction model for the closure of the palaeo asian ocean provides based on the reviewed data a tectonic model that is not only able to reasonably well explain the absence of typical collision related features in the region but also the abundance of mesozoic a type granitic magmatism in north east china

the metamorphic history of the damara orogen based on k ar data of detrital white micas from the nama group namibia abstract detrital white micas from molasse sediments of the nama group were dated by the k ar method the kuibis subgroup and the underlying pre damara sinclair sequence contain detrital muscovite with ages of 1100 1000 ma and thus cannot be derived from the damara orogen but prove to have originated from a basement probably affected by the kibaran orogeny muscovite size fractions of 250 100 m from the upper nama group upper schwarzrand and fish river subgroups yielded k ar ages 670 570 ma because these sediments are regarded as molasse series of the damara orogen these k ar ages can be interpreted as cooling ages of a first early tectono thermal event in the damara orogen a later damaran metamorphic overprint which peaked at about 530 ma is not documented in the detrital content of the nama group at the present level of erosion because detrital micas with k ar ages over 600 ma have been found up to the uppermost fish river subgroup it can be concluded that at least two tectono metamorphic events followed by uplift and erosion have taken place during the development of the damara orogen thermal alterations of the nama sediments were detected by means of illite crystallinity and k ar dating of clay size fractions these data as well as the almost exclusive occurrence of the 2m mica polytype in these size fractions point to a diagenetic to very low grade metamorphic alteration of the area investigated at about 530 500 ma and younger the deposition of the upper nama group is younger than the 570 ma detrital white micas but occurred before the 530 500 ma thermal alteration of the nama deposits the deposition of the lower nama group probably took place between 635 and 570 ma

interactive feedback between enso and the indian ocean abstract a feedback process of the indian ocean sst on enso is investigated by using observed data and atmospheric gcm it is suggested that warming in the indian ocean produces an easterly wind stress anomaly over indonesia and the western edge of the pacific during the mature phase of el nino the anomalous easterly wind in the western pacific during el nino helps a rapid termination of el nino and a fast transition to la nina by generating upwelling kelvin waves thus warming in the indian ocean which is a part of the el nino signal operates as a negative feedback mechanism to enso this indian ocean feedback appears to operate mostly for relatively strong el ninos and results in a la nina one year after the mature phase of the el nino this 1 yr period of phase transition implies a possible role of indian ocean enso coupling in the biennial tendency of the enso atmospheric gcm experiments show that indian ocean sst forcing is mostly responsible for the easterly wind anomalies in the western pacific

slab pull mantle convection and pangaean assembly and dispersal two global scale mantle convection cells presently exist on earth centred on upwelling zones in the south pacific ocean and northeast africa one cell panthalassan contains only oceanic plates the other pangaean contains all the continental plates they have remained fixed relative to one another for 400 ma a transverse rheic tethyian subduction system splits the pangaean cell poloidal plate motion in the oceanic cell reflects circumferential pull of panthalassan slabs but toroidal flow in the pangaean cell reflected by vortex type motion of continents toward the altaids of central east asia throughout the phanerozoic has resulted from the competing slab pull forces of both cells the combined slab pull effects from both cells also controlled pangaean assembly and dispersal assembly occurred during palaeozoic clockwise toroidal motion in the pangaean cell when gondwana was pulled into pangaea by the ne trending rheic subduction zone forming the appalachian variscide altaid chain pangaean dispersal occurred when the rheic trench re aligned in the jurassic to form the nw trending tethyside subduction system which pulled east gondwanan fragments in the opposite direction to form the cimmerian himalayan alpine chain this re alignment also generated a new set of indian mid ocean ridge systems which dissected east gondwana and facilitated breakup 100 200 myr long phanerozoic wilson cycles reflect rifting and northerly migration of gondwanan fragments across the pangaean cell into the rheic tethyian trench pangaean dispersal was amplified by retreat of the panthalassan slab away from europe and africa which generated mantle counterflow currents capable of pulling the americas westward to create the atlantic ocean thermal blanketing beneath pangaea and related hotspot activity were part of a complex feedback mechanism that established the breakup pattern but slab retreat is considered to have been the main driving force the size and longevity of the two cells organised and maintained by long lived slab pull forces favours deep mantle convection as the dominant circulation process during the phanerozoic

triggers of permo triassic boundary mass extinction in south china the siberian traps or paleo tethys ignimbrite flare up abstract assessment of the synchroneity between the siberian traps and the permo triassic boundary ptb mass extinction has led to the proposition that the siberian flood volcanism was responsible for the severest biotic crisis in the phanerozoic however recent studies suggest that the siberian traps may have postdated the main extinction horizon in this paper we demonstrate using stratigraphy a time and intensity coincidence between ptb volcanic ash and the main extinction horizon geochemistry of the ptb volcanic ashes in five sections in south china indicates that they were derived from continental magmatic arc zircons extracted from the ptb volcanic ashes have negative e hf t 12 9 to 2 0 and 18 o 6 8 to 10 9 consistent with an acidic volcanism and a crustal derived origin and therefore exclude a genetic link between the ptb mass extinction and the siberian traps on the basis of spatial variation in the number of the ptb volcanic ash layers and the thickness of the ash layers in south china we propose that the ptb volcanic ash may be related to paleo tethys continental arc magmatism in the kunlun area ignimbrite flare up related to rapid plate subduction during the final assemblage of the pangea super continent may have generated a volcanic winter which eventually triggered the collapse of ecosystem and ultimately mass extinction at the end of the permian the siberian traps may have been responsible for a greenhouse effect and so have been responsible for both a second pulse of the extinction event and early triassic ecological evolution

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

paleomagnetic results from triassic sections in the ordos basin north china abstract continental triassic sediments with good fossil control have been sampled in two thick sections hancheng 35 5 n 110 2 e and tongchuan 35 2 n 109 1 e from the southern margin of the ordos basin shaanxi province china detailed analysis of 633 samples coming from 69 sites has been carried out with progressive alternating field and or thermal demagnetization most sites display a low unblocking temperature component up to 200 400 c which is undistinguishable from the present earth field pef direction and a characteristic component with higher unblocking temperature with both normal and reversed polarity which differs from the pef and later mesozoic paleomagnetic directions the pole position from the lower triassic part of the hancheng section is at 61 9 n 348 3 e a 95 3 8 n 16 sites the directions of the characteristic magnetization of the middle triassic sites from the tongchuan section pass the fold test and are consistent with those from middle triassic sites of the hancheng section giving a mean paleopole at 59 8 n 359 9 e a 95 4 0 n 17 sites the late triassic sites from the tongchuan section yield a pole at 62 3 n 7 7 e a 95 3 8 n 11 sites the early triassic pole from the ordos basin is consistent with poles obtained from shanxi province a late permian to late triassic apparent polar wander path of the north china block ncb is proposed it is found that poles from the ncb and from the two adjacent blocks south china block and siberia were widely separated until at least the end of the triassic pointing to major motion between the blocks probably during the jurassic at the end of the triassic the two chinese blocks were already at similar latitudes but still were to undergo a 78 28 relative rotation both were some 38 4 to the south of siberia calculated for a reference point at 45 n 115 e on the ncb siberia boundary

geobiology and paleobiogeography tracking the coevolution of the earth and its biota abstract paleobiogeographic research is an important area of geobiology that involves the study of the coevolution of the earth and its biota by considering how tectonic and climatic changes have affected the evolution and distribution of organisms the intellectual heritage of the discipline stretches back well before darwin phylogenetic approaches to paleobiogeography have played an important part in the expansion of the field and recent analyses have incorporated geographic information systems gis each of these approaches by enhancing the precision of paleobiogeography helps make the discipline more relevant to geobiology the interaction occurring between the geological and biological sciences in paleobiogeography is apparent in several areas first there is the emergence of new techniques such as the ability to analyze ancient dna sequences also paleobiogeographers and biogeographers have realized that geo dispersal a biogeographic process first identified through studies of the fossil record can powerfully influence the evolution and distribution of biotas finally biogeographers have recognized that paleontological incompleteness and extinction constrain our ability to reconstruct biogeographic patterns in the fossil record and the extant biota respectively each of these developments suggests that further growth in paleobiogeography will involve important interactions between studies involving the fossil record and the extant biota and this along with the discipline s commitment to studying how tectonic and climatic changes have influenced evolution reaffirms the validity of the synthetic field that is geobiology

influence of the state of the indian ocean dipole on the following year s el nino el nino southern oscillation enso consists of irregular episodes of warm el nino and cold la nina conditions in the tropical pacific ocean 1 with significant global socio economic and environmental impacts 1 nevertheless forecasting enso at lead times longer than a few months remains a challenge 2 3 like the pacific ocean the indian ocean also shows interannual climate fluctuations which are known as the indian ocean dipole 4 5 positive phases of the indian ocean dipole tend to co occur with el nino and negative phases with la nina 6 9 here we show using a simple forecast model that in addition to this link a negative phase of the indian ocean dipole anomaly is an efficient predictor of el nino 14 months before its peak and similarly a positive phase in the indian ocean dipole often precedes la nina observations and model analyses suggest that the indian ocean dipole modulates the strength of the walker circulation in autumn the quick demise of the indian ocean dipole anomaly in november december then induces a sudden collapse of anomalous zonal winds over the pacific ocean which leads to the development of el nino la nina our study suggests that improvements in the observing system in the indian ocean region and better simulations of its interannual climate variability will benefit enso forecasts

the mesozoic accretionary complex in northeast china evidence for the accretion history of paleo pacific subduction abstract the mesozoic accretionary complex in northeast china which mainly consists of the jilin heilongjiang high pressure hp metamorphic belt and the nadanhada accretionary complex are the key area to understand the paleo pacific subduction accretion the jilin heilongjiang hp belt is a hp metamorphic zone between the jiamusi and songliao blocks and consists of the heilongjiang blueschist belt and the zhangguangcai complex previously published and our new geochronological data indicate that the collision between the jiamusi and songliao blocks along the jilin heilongjiang hp belt occurred between 210 and 180 ma suggesting that the jilin heilongjiang hp belt is an important unit for characterizing the geodynamic switch from the north south closure of the central asian orogenic belt to the onset of westward accretion related to subduction of paleo pacific plate in the latest triassic to early jurassic early permian igneous rocks with arc affinity in the eastern margin of the jiamusi block are more likely related to the mongol okhotsk subduction rather than the paleo pacific subduction or the collision between the jiamusi and khanka blocks as previously considered the nadanhada accretionary complex lies to the east of the jiamusi block and is composed of the yuejinshan and raohe complexes compilation of published geochronological data indicate that the yuejinshan complex was probably formed between 210 ma and 180 ma similar to ages for the jilin heilongjiang hp belt along the western margin of the jiamusi khanka block the raohe complex was formed later in the late jurassic to early cretaceous 170 137 ma likely more related to the subduction accretion of paleo pacific plate the final accretion in the target area took place in the early cretaceous 137 130 ma

geochemistry and tectonic significance of the mesoproterozoic kgwebe metavolcanic rocks in northwest botswana implications for the evolution of the kibaran namaqua natal belt the c 1 1 ga kgwebe metavolcanic rocks exposed in the northwest of botswana are late kibaran rocks they represent a bimodal suite of within plate low titanium phosphorus ltp continental tholeiites and post orogenic within plate high k rhyolites the chemical compositions of the kgwebe mafic rocks are characterized by low values of ce pb 10 and high la nb ratios average c 2 maximum 4 mid ocean ridge basalts morb normalized spidergrams show marked enrichment in mobile elements sr k rb ba and negative anomalies in nb these features suggest they may have originated in a mantle enriched during a previous subduction event the kgwebe metarhyolites are marked by y 60 ppm sr y 20 and high k contents they cannot therefore be the product of melting of sediments or a subducting slab it is inferred that they represent felsic magmas resulting from melting of mesoproterozoic kibaran calcalkaline rocks underplated in the middle and or lower crust the kgwebe bimodal metavolcanic rocks pre date the neoproterozoic ghanzi group rocks which are correlated with the lower part of the damara sequence the chemical composition and field relations suggest that these metavolcanic rocks were emplaced during a late orogenic collision associated extensional collapse this collapse affected a crust thickened during the kibaran orogeny in the namaqua natal belt of southwest africa

geochronology of mesoproterozoic hybrid intrusions in the konkiep terrane namibia from passive to active continental margin in the namaqua natal wilson cycle abstract this work investigates a number of gabbro granite hybrid rocks exposed in the great escarpment between the coastal namib desert and the inland plateau of namibia they form part of the tectonostratigraphic konkiep terrane which lies between the mesoproterozoic namaqua natal province and largely palaeoproterozoic rehoboth province in southern africa microbeam u pb and lu hf analyses of zircon were used to investigate the geochronology of these rocks which have previously been assigned to the mooirivier metamorphic complex or the kairab formation the oldest hybrid rocks at neuhof valley are u pb dated at 1359 6 ma and cut by 1347 8 ma unfoliated granite dykes but have the youngest lu hf crustal residence ages between 1690 and 1430 ma together with nearby volcanic rocks of the 1333 6 ma neuhof and 1327 10 ma welverdiend formations which we dated they are thought to reflect rifting of the rehoboth province followed by the ocean development by seafloor spreading phase of the namaqua wilson cycle the hybrid rocks at goede hoop foothills are u pb dated at 1230 6 ma with a number of xenocrysts up to 1532 ma similar hybrid rocks at hauchabfontein have 20 30 ma younger u pb ages of 1211 19 ma and 1202 7 ma two samples they formed by gabbro intruding an 1195 5 ma granite within error but older from field relations and contain many xenocrysts with u pb ages 1755 29 ma n 7 1367 and 1260 17 ma n 24 all the goede hoop foothills and hauchabfontein hybrid rocks have old lu hf crustal residence ages from 1935 to 2000 ma and one sample up to 2320 ma reflecting involvement of palaeoproterozoic rehoboth province crust this 1230 to 1200 ma group of hybrid rocks corresponds in age to the arc magmatism recognised in the namaqua natal province to the west and south of the konkiep terrane the hybrid rocks probably formed during the closure of the namaqua ocean by eastward subduction under the rehoboth province corresponding to the previously proposed rehoboth magmatic arc and forming the konkiep terrane by massive intrusions into the margin of the rehoboth province the hybrid rocks we investigated in the konkiep terrane are thus related to the rifting phase and the pre collisional subduction phase of the namaqua wilson cycle the arc related magmatism ended abruptly at 1200 ma as the namaqua natal terranes were assembled by collisions and subduction ceased we did not find evidence for the 1200 to 1150 ma post collisional metamorphic cycle and magmatism which prevailed in the adjacent grunau terrane of the namaqua province suggesting that the konkiep terrane did not experience crustal thickening during the namaqua collision and terrane assembly an undeformed felsic lava at sukses which we dated at 1105 10 ma corresponds in age to the langberg formation in the rehoboth terrane it is coeval with the keimoes suite of post tectonic intrusions and younger koras lavas in the namaqua natal province and these 1100 ma rocks all extend the area of the plume related umkomdo large igneous province documented on the kaapvaal craton this part of the konkiep terrane originated in the rehoboth province and was then modified by magmatic intrusions coupled to the evolution of the namaqua natal province

permian stratigraphy and correlation of northeast china a review palaeontological lithostratigraphical data from the permian strata and correlation of the permian successions for different tectonic units in northeast china are reviewed and summarized in this paper permian strata in northeast china are dominated by brachiopods fusulinoideans and land plants with limited ammonoids conodonts and bivalves the cisuralian early permian in the northern margin of the north china block and in the manchuride belt is composed mostly of marine massive limestone with the characteristic pseudoschwagerina zone in the asselian and sakmarian and the misellina claudiae zone in the kungurian the cisuralian in the xing an block and the northeastern part of inner mongolia is dominated by huge terrestrial deposits with fossil plants the guadalupian middle permian in the manchuride altaid and yanbian belts are characterized by bi temperate roadian or early wordian monodiexodina fauna and the late wordian capitanian codonofusiella schwagerina or neoschwagerina yabeina faunas the mixed brachiopod faunas between the boreal antitropical and the palaeoequatorial cathaysian forms the roadian or early wordian solitary coral faunas and the late wordian capitanian compound waagenophyllum wentzelella fauna the nadanhada terrane contains some exotic limestone blocks with a typical cathaysian neoschwagerina yabeina fauna in a late jurassic early cretaceous melange which is related to mesozoic subduction in the western circum pacific region the lopingian late permian in northeast china is mostly characterized by terrestrial molasse deposits with a mixed flora between the boreal angaran and the palaeoequatorial cathaysian provinces indicating the final closure of the palaeo asian ocean c 2005 elsevier ltd all rights reserved

late paleozoic to early triassic multiple roll back and oroclinal bending of the mongolia collage in central asia abstract the architecture and mechanics of an orogen can be understood in terms of a system of collages that are characterized by a complex assemblage of multiple components but the fundamental paleogeographic framework and the tectonic relationships between the different components are often insufficiently defined because of unavailable data the central asian orogenic belt caob provides an ideal opportunity to address the fundamental framework of paleogeography and tectonic relationships between the diverse and many components in this huge collage in this paper we review several lines of available evidence which enable us to propose a new tectonic model of huge roll back in the formation of the accretionary tectonics of the mongolian collage in central asia in the early paleozoic the mongolia collage comprised the southern siberian and the tuva mongol oroclines the siberia craton and the mongolia collage jointly formed a giant tadpole shape within the paleo asian and panthanlassic oceans its head siberia was to the south and the tail tuva mongol to the northwest the structures and tectonic zonation of the mongolia collage are characteristic of multiple arcs which have been separately described in detail in different segments southwards from the southern siberia east sayan west sayan gorny altai chara via the lake zone junggar tianshan gobi altai beishan alxa to the manlay hegenshan baolidao solonker segments almost all segments underwent early paleozoic to permian or even triassic frontal subduction and accretion while rifting in the late carboniferous to permian or triassic occurred in the outward oceanward westward advancing mongolian collage therefore we suggest that a huge complex roll back active from the carboniferous to permian or even to late triassic facilitated the formation of the mongolian collage the outward multiple roll back process was compatible and almost coeval with the start of the tuva mongol orocline and rotation of the siberian craton as confirmed by paleomagnetic and structural data during the roll back processes an archipelago paleogeography was formed behind the frontal subduction and accretion in which independent arcs or terranes were amalgamated or collided to form composite arcs or terranes either simultaneously or at slightly different times the roll back process was affected by the collision of the kazakhstan collage along the chara and karamay zones in the early permian the collision of the tarim craton along the south tianshan zone in the early permian the collision of the dunhuang block along the liuyuan zone in the early permian triassic the collision of the alxa block along the qugan qulu zone in the permian and the collision of the north china craton along the solonker zone in the middle late triassic the tectonic styles and architecture of accretionary orogenic belts like the caob are characterized both by the amalgamation of multiple terranes and by oroclinal bending the systematic anatomy of the multiple roll back processes and their interactions with the adjacent collages shed light on the evolving orogenic architecture and the crustal accretionary history of orogens

paleozoic terranes of eastern australia and the drift history of gondwana abstract critical assessment of paleozoic paleomagnetic results from australia shows that paleopoles from locations on the main craton and in the various terranes of the tasman fold belt of eastern australia follow the same path since 400 ma for the lachlan and thomson superterranes but not until 250 ma or younger for the new england superterrane most of the paleopoles from the tasman fold belt are derived from the lolworth ravenswood terrane of the thomson superterrane and the molong monaro terrane of the lachlan superterrane consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic australia by the late early devonian the lolworth ravenswood terrane is interpreted to have undergone a 90 clockwise rotation between 425 and 380 ma although the tamworth terrane of the western new england superterrane is thought to have amalgamated with the lachlan superterrane by the late carboniferous geological syntheses suggest that movements between these regions may have persisted until the middle triassic this view is supported by the available paleomagnetic data with these constraints an apparent polar wander path for gondwana during the paleozoic has been constructed after review of the gondwana paleomagnetic data the drift history of gondwana with respect to laurentia and baltica during the paleozoic is shown in a series of paleogeographic maps

ophiolites in the xing an inner mongolia accretionary belt of the caob implications for two cycles of seafloor spreading and accretionary orogenic events the xing an inner mongolia accretionary belt in the southeastern segment of the central asian orogenic belt caob was produced by the long lived subduction and eventual closure of the paleo asian ocean and by the convergence between the north china craton and the mongolian microcontinent two ophiolite belts have been recognized the northern erenhot hegenshan xi ujimqin ophiolite belt and the southern solonker linxi ophiolite belt most basalts in the northern ophiolite belt exhibit characteristics of normal type to enriched type mid ocean ridge basalt affinities with depleted nd isotopic composition epsilon nd t 5 comparable to modern eastern pacific mid ocean ridge basalts most basaltic rocks in the southern belt show clear geochemical features of suprasubduction zone type oceanic crust probably formed in an arc back arc environment the inferred back arc extension along the solonker linxi belt started at circa 280 ma statistics of all the available age data for the ophiolites indicates two cycles of seafloor spreading subduction which gave rise to two main epochs of magmatic activity at 500 410 ma and 360 220 ma respectively with a gap of similar to 50 million years myr the spatial and temporal distribution of the ophiolites and concurrent igneous rocks favor bilateral subduction toward the two continental margins in the convergence history with final collision at similar to 230 220 ma in the whole belt signals of continental collision and himalayan style mountain building are lacking we thus conclude that the xing an inner mongolia segment of the caob experienced two cycles of seafloor subduction back arc extension and final appalachian type soft collision

permo triassic magnetostratigraphy in china the type section near taiyuan shanxi province north china summary a palaeomagnetic study has been made of samples collected from the permo triassic type section near taiyuan shanxi province in the north china block no results were obtained from the upper carboniferous shanxi and taiyuan formations results from the permian lower and upper shihezi and shiqianfeng formations and from the lower triassic liujiagou formation were restricted mainly to the red shale and red mudstone horizons that were preferentially sampled for this study after thermal demagnetization the following pole positions were obtained lower permian lower shihezi formation n 11 samples 20 9 n 1 4 e with dp 6 1 and dm 12 2 upper permian combined upper shihezi and shiqianfeng formations n 89 samples 47 8 n 357 4 e with dp 2 3 and dm 4 3 lower triassic liujiagou formation n 25 samples 50 0 n 351 o e with dp 3 7 and dm 7 0 the sequence crosses the younger boundary of the permo carboniferous reversed kiaman superchron and the polarity sequence observed suggests that this superchron ended in mid ufimian times a minimum of 13 polarity zones seven normal and six reverse then follow before the permo triassic boundary this is in excellent agreement with currently available observations worldwide

evolution of a permian intraoceanic arc trench system in the solonker suture zone central asian orogenic belt china and mongolia abstract the identification of a fossil arc trench system from the ophiolite decorated solonker suture zone in the southernmost central asian orogenic belt caob enables us to constrain the timing of pre subduction extension ca 299 290 ma subduction initiation ca 294 280 ma ridge trench collision ca 281 273 ma and slab break off ca 255 248 ma in the permian a fraction of proto arc crust ca 45 km long up to 8 km wide is preserved as a volcanic plutonic sequence and is juxtaposed against a wide ca 30 80 km forearc melange this proto arc crust comprises two distinct magma series island arc tholeiite iat and mid ocean ridge basalt morb both of which have strong supra subduction zone ssz geochemical signatures zircons from a gabbro and a plagiogranite yielded weighted mean 206pb 238u ages of 284 0 4 0 and 288 0 6 0 ma the forearc melange consists of numerous ophiolite fragments and continental margin derived olistoliths blocks that predate the ophiolite the olistoliths are best represented by a gabbroic block 291 8 2 3 ma that contains granite xenoliths 312 6 1 8 and 313 6 3 1 ma other dated blocks include a trondhjemite 323 9 2 7 ma a gabbro 296 6 1 7 ma and a tonalite 294 9 2 4 ma small bodies of diabase andesite and diorite in the forearc melange exhibit a wide variety of geochemical signatures we dated zircons from an n morb like diabase 274 4 2 5 ma an e morb like diabase 252 5 2 3 ma a transitional sanukitoid adakite andesite 250 2 2 4 ma a sanukitoid high mg diorite 251 8 1 1 ma and an anorthosite 252 2 1 7 ma the n morb like diabase contains ca 301 394 ma zircon xenocrysts suggesting assimilation of trench sediments when a spreading ridge intersected a trench the other dated rocks simultaneously formed near the permian triassic boundary and captured abundant zircon xenocrysts ca 269 295 ma ca 301 495 ma and ca 923 2501 ma our new formation ages constrain a magmatic episode in response to slab break off beneath a fossil forearc in a young post collisional setting and the youngest xenocryst ages ca 269 273 ma may define the maximum depositional age of trench sediments

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

paleomagnetism of the 1 1 ga umkondo large igneous province in southern africa 1 the umkondo dolerites are present over a wide area in the kalahari craton southern africa thirty nine sampling sites in botswana and south africa yielded tightly grouped paleomagnetic directions due south with shallow inclinations and three sites of opposite polarity the dolerites have u pb single crystal baddeleyite or zircon crystallization ages of 1112 0 5 to 1108 0 9 ma these results can be combined with published data from 39 additional umkondo sites and 33 sites in the grunehogna province of antarctica after restoring east antarctica to its position next to southern africa grouping the sites geographically yields 10 site mean poles with mean at 64 0 n 38 8 e a95 3 7 this umkondo pole can be correlated with keweenawan poles from laurentia because both sets of poles are precisely of the same age as well as predominantly of one polarity the relative orientation of the two cratons within the rodinia supercontinent is fixed this implies that the namaqua natal maud belt which rims the southern part of the kalahari craton faced away from laurentia the umkondo pole combined with published poles suggest that the kalahari craton remained distinctly south of the laurentian craton between 1 1 and 1 0 ga making it highly unlikely that the two cratons collided

the koras sinclair ghanzi rift in southern africa volcanism sedimentation age relationships and geophysical signature of a late middle proterozoic rift system abstract a number of relatively undeformed late middle proterozoic volcano sedimentary basins are aligned along the western and northern margins of the kalahari craton although the assemblages of these basins have been compared and lithologically correlated by many authors radiometric ages partly contradict these interpretations attempts to incorporate all of these basins into a regional structural interpretation have been rare watters magmatic arc interpretation is contradicted by the overall geochemistry of the volcanic rocks the coarse continental red bed sediments and the structural style of the basins the depositional troughs were narrow fault bounded continental rift grabens with a structural style and sedimentation pattern controlled by strong vertical tectonism the development of the basins along two branches of a propagating continental rift system the koras sinclair ghanzi rift ksg rift is proposed radiometric ages reveal a distinct younging along the rift from the southern toward the northeastern branch the geophysical signature of the rift is dominated by positive bouguer gravity anomalies flanked by gravity lows which follow a linear trend the basins contain distinctly bimodal volcanic rocks with some intermediate volcanics in the sinclair basin contemporaneous with the extrusion of the volcanics granitic high level intrusions were emplaced along the rift the possible existence of a northern coastal branch of the ksg rift and the location of a triple junction is discussed the rift process possibly continued and led to the development of the early damara rift in swa namibia the african plate kalahari and congo cratons migrated southward between 1050 and 950 ma ago a stationary mantle plume probably caused the development of both the ksg and damara rift a comparison with rift migration in kenya is drawn the regional trends and structures of the ksg rift were reactivated several times undergoing both extension and compression the most prominent of these events was the development of the damara orogen which followed the regional trend of the late middle proterozoic rift but fault structures have been reactivated up to recent times

evolution of the mongol okhotsk ocean as constrained by new palaeomagnetic data from the mongol okhotsk suture zone siberia summary this paper presents new data from palaeomagnetic investigations on the upper palaeozoic and mesozoic geological units from the siberian platform and the mongol okhotsk suture zone within the southern portion of the mongol okhotsk suture we collected palaeomagnetic samples from the late permian belektuy formation borzya region 50 7un 116 9ue and the middle late jurassic shadaron formation unda daya 51 5un 117 5ue we sampled the late permian alentuy formation khilok region 50 8un 107 2ue the early to middle jurassic irkutsk sedimentary basin isb 52 0un 104 0ue the late jurassic badin formation mogzon region 51 8un 112 0ue and the early cretaceous gusinoozesk formation gusinoe lake region 51 2un 106 5ue additionally in the northern region of the mongol okhotsk suture apart from the results of the isb and gusinoozersk formations which show very large ellipses of confidence and might be the present day geomagnetic field overprint our results allow us to constrain the evolution of the mongol okhotsk ocean palaeomagnetically from the late permian to the middle late jurassic they confirm that this large permian ocean closed during the jurassic ending up in the late jurassic or the beginning of the cretaceous in the eastern end of the suture zone as suspected on geological grounds however although geological data suggest a middle jurassic closure of the mongol okhotsk ocean in the west trans baikal region our data show evidence of a still large palaeolatitude difference between the amuria and siberia blocks this is interpreted as a result of the quite fast closure of the ocean after the middle jurassic finally our new palaeomagnetic results exhibit very large tectonic rotations around local vertical axes which we interpret as probably arising both from collision processes and from a left lateral shear movement along the suture zone due to the eastward extrusion of mongolia under the effect of the collision of india into asia

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

preliminary early cretaceous paleomagnetic results from the gansu corridor china we report results from our paleomagnetic study of lower cretaceous redbeds from the gansu corridor northwestern china the characteristic remanent magnetization chrm resides in hematite often at very high unblocking temperatures 660 c the directions associated with this component exhibit only reversed polarities from locality a sunan area but the samples from locality b lanzhou area 480 km to the southeast show roughly antipodal normal and reversed polarities the combined sample directional data from both localities pass a fold test at the 99 confidence level the mean paleomagnetic pole is located at 48 7 n 199 7 e with a 95 4 1 which is discordant with poles of similar age elsewhere from neighboring regions in china although represented by relatively few samples n 21 this pole suggests that significant post cretaceous motion may have occurred between the gansu corridor and adjacent blocks relative to eurasia or north china the discordance corresponds to 28 1 5 2 or 35 6 9 7 clockwise rotation and 9 5 4 5 or 9 8 8 2 northward displacement respectively the rotations support but do not yet distinguish between several neotectonic models assumed to have acted over the past 15 40 m y the displacement is not predicted by any of these models if real it may have occurred early in the history of the india asia collision or even before

did the paleo asian ocean between north china block and mongolia block exist during the late paleozoic first paleomagnetic evidence from central eastern inner mongolia china 1 the tectonic evolution of the paleo asian ocean between the north china block ncb and the mongolia block mob is a contentious issue and geodynamic models remain speculative in an effort to puzzle out this controversy a paleomagnetic study was carried out on the silurian to permian formations in central eastern inner mongolia china more than 680 sedimentary and volcanic samples were collected from 86 sites we have established titanium poor magnetite and hematite as the principal magnetic carriers anisotropy of the magnetic susceptibility measurements demonstrate negligible deformation of the majority of study rocks with sedimentary fabrics from primary magnetizations a late devonian and a permian pole are calculated for inner mongolia block imb at 46 8 n 349 1 e dp 14 6 dm 27 3 with n 3 and 48 7 n 3 7 e dp 5 2 dm 9 1 with n 6 respectively two stages of secondary magnetization are also identified probably due to early permian and early cretaceous magmatic events as preliminary results the comparison of our new paleomagnetic poles with available data from ncb mob and siberia indicates that 1 the paleolatitudes of imb ncb and mob are consistent between late devonian and permian suggesting pre late devonian closure of the paleo asian ocean and further evaluation of these three blocks as a single entity and 2 post permian intracontinental deformation was significant and characterized by block rotations which are due to strike slip faulting within the welded ncb imb mob block

paleomagnetic constraints on the paleogeography of the east asian blocks during late paleozoic and early mesozoic times abstract although the axial and dominant geocentric character of the earth s magnetic field means that paleolongitude is indeterminate paleomagnetism is otherwise the only truly quantitative method available to the earth scientist for constraining paleogeography and reconstructing the kinematic evolution of continental blocks during the past half century numerous paleomagnetic results have provided substantial quantitative constraints on the origin and tectonic evolution of the major tectonic divisions now comprising eastern asian in this paper we first assess the available early paleozoic to early cretaceous paleomagnetic results from the south china north china and tarim blocks using internationally recognized reliability criteria we then construct a running mean through a 20 ma window by weighting the poles according to their q factors and fit a spherical spline with smoothing factor of 300 to derive apparent polar wander apw paths for these three major blocks during this early paleozoic to late mesozoic time interval together with late paleozoic to early mesozoic paleomagnetic poles from the qaidam qiangtang lhasa sibumasu indochina and some other smaller blocks terranes of east asia we produce a series of paleogeographic reconstructions for these major blocks and lesser terranes of east asia between mid ordovician and late jurassic times 460 160 ma which although based primarily upon paleomagnetic evidence aim to embrace the geological constraints finally we discuss the current evidence for closure times of the paleo asian mianlue and east paleo tethyan oceans which incorporate fundamental issues concerning the formation of the east asian continental collage and collision with the northern main body of the pangean supercontinent we use the collective evidence to argue that these major paleo oceans had closed by the late triassic and that the east asian sector of the supercontinent had united to become an integral part of pangea by that time 220 ma

provenance analysis of the late paleozoic sedimentary rocks in the xilinhot terrane ne china and their tectonic implications abstract the xilinhot terrane is located in the eastern segment of the central asian orogenic belt in ne china and is a key to a hotly debated issue on the paleozoic tectonic evolution of this giant progenic belt to constrain the tectonic evolution of the xilinhot terrane in the late paleozoic we undertook zircon u pb dating and geochemical analyses of the zhesi and benbatu formations in the suolun and xi ujimqin areas in the xilinhot terrane samples of the benbatu formation yield detrital zircon u pb ages ranging from 2659 ma to 316 ma with four age populations at 2659 1826 ma 1719 963 ma 590 402 ma and 396 316 ma whereas samples from the zhesi formation yield detrital zircon u pb ages ranging from 1967 ma to 250 ma with four age populations at 1967 1278 ma 971 693 ma 561 403 ma and 399 250 ma the age groups of both the benbatu and zhesi formations in the xilinhot terrane are similar to those in other parts of the central asian orogenic belt caob this evidence indicates that the xilinhot terrane is a microcontinent and not an accretionary complex as previously thought furthermore the youngest zircon grains in the benbatu and zhesi formations yield weighted mean 206 pb 238 u ages of 322 12 ma msdw 0 12 n 4 and 257 2 8 ma msdw 1 6 n 8 respectively combined with fossil data our new data suggest that the benbatu and zhesi formations in the xilinhot terrane were possibly deposited at 322 ma and 257 ma respectively based on the provenance of the carboniferous permian sandstones came from the blocks of ne china we speculate that the xilinhot terrane is the western part of the songliao block

evolving core conditions ca 2 billion years ago detected by paleosecular variation abstract paleomagnetic data provide one of the few probes available to interrogate early evolution of the core here we apply this probe by examining the latitudinal dependence of paleosecular variation psv data derived from high quality paleomagnetic data collected from proterozoic and neoarchean rocks these data define a neoarchean geomagnetic field that was more dipolar than that during proterozoic times indicating a change in core conditions the signals observed may reflect a change in forcing of the dynamo and an early onset of inner core growth we propose a model that links evolution of the core mantle and crust in three principal phases i before approximately 3 5 ga an entirely liquid core may not have hosted a geodynamo if heat transport was sufficient across the core mantle boundary however a geodynamo could have been generated if so sources in the shallow outer core could have been more important for generating the dynamo relative to deeper convection resulting in a field that was less dipolar than that generated in later times ii cooling of the lower mantle between ca 2 and 3 5 billion years ago was promoted by deep subduction and possibly coincided with inner core growth the geodynamo during this episode was deeply seated producing a highly dipolar surface magnetic field iii after ca 2 billion years ago continued subduction led to large scale core mantle boundary compositional and heat flux heterogeneity with these changes shallow core contributions to the geomagnetic field grew in importance resulting in a less dipolar field

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

the pre devonian tectonic framework of xing an mongolia orogenic belt xmob in north china abstract a new tectonic division of the xing an mongolia orogenic belt xmob in north china has been presented according to our research and a lot of new data of tectonics geochronology and geochemistry four blocks and four sutures have been recognized in the xmob including the erguna eb xing an airgin sum xab songliao hunshandake shb and jiamusi jb and xinlin xiguitu xxs xilinhot heihe xhs mudanjiang ms and ondor sum yongji sutures oys the framework of the xmob is characterized by a tectonic collage of the blocks and orogenic belts between them different precambrian basements have been found in the blocks including the neoproterozoic metamorphic rocks and plutons in the eb the neoproterozoic metamorphic rocks in western and eastern of segments of the xab mesoproterozoic and neoproterozoic metamorphic rocks in middle segments of the xab respectively the neoproterozoic metamorphic rocks and mesoproterozoic volcanic rocks and plutons in the shb and neoproterozoic metamorphic rocks in the jb the xxs resulted from a northwestward subduction of the xab beneath the eb during the cambrian which was followed by the forming of the xhs and oys in the northwest and south margins of the shb in the silurian respectively the ms was caused by a westward subduction of the jb beneath the east margin of the shb during the middle devonian the three cambrian silurian and middle devonian events indicate that the xmob belongs to a pre middle devonian multiple orogenic belt in the central asian orogenic belt caob forming of the xmob suggests that the southeast part of the paleo asian ocean closed before the middle devonian

cratonic reactivation and orogeny an example from the northern margin of the north china craton abstract reactivation of cratonic basement involves a number of processes including extension compression and or lithospheric delamination the northern margin of the north china craton ncc adjacent to the inner mongolian orogenic belt was reactivated in the late paleozoic to early mesozoic during this period the northern margin of the ncc underwent magmatism n s compression regional exhumation and uplift including the formation of e w trending thick skinned and thin skinned south verging folds and south verging ductile shear zones zircon u pb shrimp ages for mylonite protoliths in shear zones which show ages of 310 290 ma mid carboniferous early permian constraining the earliest possible age of deformation muscovite within carbonate and quartz feldspar muscovite mylonites from the kangbao weichang and fengning longhua shear zones defines a stretching lineation and gives 40ar 39ar ages of 270 250 ma 250 230 ma 230 210 ma and 210 190 ma deformation developed progressively from north to south between the late paleozoic and triassic exhumation of lower crustal gneisses high pressure granulites and granites occurred at the cratonic margin during post ductile shearing 220 210 ma an undeformed early jurassic 190 180 ma conglomerate overlies the deformed rocks and provides an upper age limit for reactivation and orogenesis deformation was induced by convergence between the southern mongolia and north china cratonic blocks and the location of this convergent belt controlled later deformation in the yanshan tectonic province this province formed as older e w trending archean proterozoic sequences were reactivated along the northern margin of the ncc this reactivation has features typical of cratonic basement reactivation compression crustal thickening remelting of the mid to lower crust and subsequent orogenesis adjacent to the orogenic belt

oligo miocene magnetostratigraphy and rock magnetism of the xishuigou section subei gansu province western china and implications for shallow inclinations in central asia magnetostratigraphy of 222 remanent directions together with late oligocene to early miocene mammal and charophyte paleontology suggest that 2179 m of the xishuigou section subei gansu province china were deposited from 26 to 19 ma stratigraphic patterns of bulk susceptibility anisotropy of magnetic susceptibility parameters and natural and anhysteretic remanent magnetization intensities demonstrate that 1 faulting does not significantly affect the record 2 sediment deposition was relatively continuous 3 sediment source changed around 23 ma and 4 rapid uplift near subei occurred at 21 ma subei rotated 27 5 counterclockwise with respect to the 20 ma pole from the eurasian synthetic apparent polar wander path folding and rotation of the section took place after 19 ma the paleolatitude of subei is 14 less than at present and 19 3 less than predicted from the reference pole both rock magnetic and paleomagnetic data sets suggest that the unusually low paleolatitude is the result of synsedimentary inclination shallowing a phenomenon which has likely affected other paleomagnetic data from central asia

geodynamics of the western part of the mongolia okhotsk collisional belt trans baikal region russia and mongolia abstract after the western edge of the mongolian microcontinent joined the siberian continent in the region of central mongolia in the earliest permian these two continental blocks remained turned at an angle of about 120 with respect to each other and separated on greater extent of their present day boundary by an enormous gulf of the paleopacific called the mongolia okhotsk ocean closure of this ocean at the early middle jurassic boundary led to the complete collision of siberia and mongolia which by then had already become part of the mongolia north china continent this main collisional episode which lasted through the middle and late jurassic involved thrusting folding and magmatism and produced the mongolia okhotsk belt the onon island arc which was located in the mongolia okhotsk ocean was squeezed between the two major continents inasmuch as the third element the island arc was involved in the collision it is reasonable to distinguish two branches of the mongolia okhotsk suture these branches control the spatial distribution of gold mineralization in the trans baikal region on the southeastern periphery of siberia the crust thickened considerably after the collision and a plateau like uplift formed in the early cretaceous when compression ceased the collisional uplift collapsed and the thrusts were transformed into low angle normal faults the motions on which were responsible for the formation of rift basins and exhumation of metamorphic core complexes

late palaeozoic to triassic evolution of the turan and scythian platforms the pre history of the palaeo tethyan closure abstract a number of en echelon arranged southwest facing arc fragments of palaeozoic to jurassic ages sandwiched between two fairly straight east northeast trending boundaries constitute the basement of the scythian and the turan platforms located between the laurasian and tethyside units they have until now largely escaped detection owing to extensive jurassic and younger cover and the inaccessibility of the subsurface data to the international geological community these units are separated from one another by linear gently curved faults of great length and steep dip those that are exposed show evidence of strike slip motion the arc units originally constituted parts of a single silk road arc located somewhere south of the present day central asia for much of the palaeozoic although by the late carboniferous they had been united into a continental margin arc south of the tarim basin and equivalent units to the west and east they were stacked into their present places in northern afghanistan turkmenistan caucasus and the northern black sea by large scale right lateral strike slip coastwise transport along arc slicing and arc shaving strike slip faults in the triassic and medial jurassic simultaneously with the subductive elimination of palaeo tethys this gigantic dextral zone the silk road transpression was a trans eurasian structure and was active simultaneously with another similar system the gornostaev keirogen and greatly distorted eurasia the late palaeozoic to jurassic internal deformation of the dniepr donets aulacogen was also a part of the dextral strain in southern europe when the emplacement of the scythian and turan units was completed the elimination of palaeo tethys had also ended and neo tethyan arcs were constructed atop their ruins mostly across their southern parts the western end of the great dextral zone that emplaced the turan and scythian units horsetails just east of north dobrudja and a small component goes along the tornquist teisseyre lineament

evolution of the solonker suture zone constraints from zircon u pb ages hf isotopic ratios and whole rock nd sr isotope compositions of subduction and collision related magmas and forearc sediments abstract the solonker zone in northern inner mongolia china is considered as the suture between the north china craton and the south mongolian microcontinent two magmatic belts are recognized along the suture zone a subduction related magmatic belt represented by the baolidao arc rocks and a younger collision related granite belt represented by the halatu granites we use zircon u pb ages zircon in situ hf isotopic analyses and whole rock nd sr isotopic data of the two magmatic belts and related forearc sediments the xilinhot metamorphic complex to constrain timing of the suturing and to discuss the petrogenesis of the magmatic rocks a gabbroic diorite bld 1 of the baolidao arc was dated at 310 5 ma by shrimp this sample shows an e nd t value of 2 5 and i sr of 0 7052 hf isotopic analyses on 25 zircons from the same sample show e hf t 5 4 to 11 5 another diorite sample xh 2 of the same arc from south of xilinhot displays even more depleted isotopic compositions with e nd t 5 6 and i sr 0 7037 the main population of zircons from this sample have highly variable and depleted hf isotopic compositions e hf t 0 18 3 the large variation in hf isotopic composition of zircons with largely the same crystallization age from a single pluton is explained by a mixing process between depleted mantle derived magma and continental crust in an active continental arc setting the halatu granite hlt 2 was dated at 234 7 ma by shrimp zircons from the granite also show a large variation of e hf t values 9 1 to 26 despite most samples having whole rock e hf t 2 the large variation in e hf t values suggests that the granite formed probably by partial melting of two source regions a dominant juvenile crust and a subordinate old continental crust most zircons from the xilinhot metamorphic complex show ages comparable with those of the baolidao arc rocks suggesting that the protolith of the metamorphic complex was probably deposited during or after arc magmatism some zircons however show precambrian ages that fall into two groups one with ages of 780 900 ma resembling those from the south mongolian microcontinent and the other with ages of 1524 2900 ma similar to those of the north china craton thus the protolith of the metamorphic complex probably formed in a forearc basin during convergence of the two continents and metamorphosed subsequently during collision in the late paleozoic our zircon age data thus constrain timing of collision between the south mongolian microcontinent and the north china craton to have been between 296 and 234 ma

interdecadal change in the relationship between enso and the intraseasonal oscillation in east asia abstract the northward propagating intraseasonal oscillation npiso during the boreal summer is closely linked to the onset retreat and intensity of the east asian summer monsoon easm in this study interdecadal variability in the relationships between the npiso and el nino southern oscillation enso was investigated using long term outgoing longwave radiation data obtained from the 40 yr ecmwf re analysis era 40 for a 44 yr period 1958 to 2001 it was found that before the late 1970s the preceding winter enso influenced the early summer i e may to june npiso activity whereas after the late 1970s a strong relationship appeared during the later summertime i e july to august the may june npiso before the late 1970s was modulated by springtime indian ocean sea surface temperature warming and central north pacific suppressed convection anomalies and was consequently related to the enso induced west pacific wp pattern which shows a north south dipole structure over the north pacific from

the zonal dipole pattern of tropical cyclone genesis in the indian ocean influenced by the tropical indo pacific ocean sea surface temperature anomalies abstractfrom a basinwide perspective the dominant mode of indian ocean tropical cyclone genesis tcg in september november son shows an equatorially symmetric east west zonal dipole pattern wh

relationship between enso and northward propagating intraseasonal oscillation in the east asian summer monsoon system 1 observational studies are presented on the relationship between el nino southern oscillation enso and the northward propagating intraseasonal oscillation npiso in the east asian summer monsoon easm system the summer npiso activity shows a significant correlation with the preceding winter extreme phase of enso cycles a higher correlation appears during late summer which is consistent with frequent heavy rainfall events at that time as revealed in some previous case studies the westward expansion of broad anticyclonic circulation over the western north pacific and the smaller cyclonic circulation around korea and japan are found to be associated with the npiso activity enso affects the late summer npiso activity through an atmospheric bridge and wave propagation the springtime indian ocean sea surface temperature warming induced by enso through the walker circulation leads to the downward motion and suppressed convection over the philippine sea and this generates the forced rossby wave train forming the above south to north low level circulation anomalies

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

fragmentation of asia in the permian asia is a composite continent formed by the accretion of crustal blocks1 3 a likely sequence of events is that siberia collided with a kazakhstan block which together then collided with europe along the urals in permo triassic times2 this was followed by the sucessive accretion of various blocks of south and east asia to siberia culminating in the collision of india with asia during the cenozoic palaeomagnetic data have already demonstrated that the kolyma and sikhote alin blocks of eastern asia collided with the main continent along the late mesozoic fold belts of verkhoyansk and sikhote alin4 furthermore results from the malay peninsula5 and japan6 suggest that south east asia and japan were situated near the equator in permian times and were therefore separated from the asian continent we report here some palaeomagnetic results from the permian of the sino korean and yangtze blocks of china that show they were also situated near the equator were not in their present relationship to one another and were widely separated from siberia

interbasin coupling between the tropical indian and pacific ocean on interannual timescale observation and cmip5 reproduction the interaction of el nino southern oscillation enso with tropical indian ocean s two major modes i e indian ocean dipole iod and indian ocean basinwide mode iobm is of great importance to understanding global climate variability using observational data for the last 50 years and the phase five of coupled model intercomparison project cmip5 historical simulation for the last 100 years this study investigates the role of interbasin coupling between the indian and pacific ocean on el nino evolution analyses suggest that the combined effect of the iod during the developing el nino phase and the iobm during the decaying phase plays a critical role in leading a fast transition from el nino to la nina in particular a faster iod termination and predominant iobm in the el nino winter result in prevailing easterly wind anomalies through the eastern indian ocean to the western pacific countervailing the iod related westerly wind anomalies over the western pacific the significant easterly wind anomalies then contribute to the maintenance of the western north pacific subtropical high anomalies until the el nino decaying summer consequently facilitating rapid termination of el nino and transition to la nina meanwhile the sole effect of either iod or iobm causes a slow decay of el nino the 20 cmip5 models generally capture the role of interbasin coupling on the el nino evolution in spite of models common deficiencies in simulating the easterly wind anomalies after decay of iod the late iod demise might cause weaker el nino phase transition in models due to the longer lasting destructive interference between iod and iobm related western pacific wind anomalies this study indicates that challenges still remain in better simulations of the various aspects of interbasin indo pacific coupling and then a diversity of the enso life cycle

a middle permian ophiolitic melange belt in the solonker suture zone western inner mongolia china implications for the evolution of the paleo asian ocean

geomagnetic secular variation and the statistics of palaeomagnetic directions in this study we examine the role of palaeosecular variation psv in the use of statistics for palaeomagnetic studies and we provide new reliability criteria for palaeomagnetic poles or directions we first conclude that fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole vgp distributions instead secondly we strongly advocate that typical properties of geomagnetic field behaviour are taken into account in the assessment of palaeomagnetic data sets the latitude dependent properties e s k provide useful guidelines for the reliability of a palaeomagnetic data set a reliable assessment of these properties depends on the sufficient number of palaeomagnetic samples being taken therefore as an additional instrument of assessing data sets we provide a n dependent a95 envelope bounded by an upper limit a95max and a lower limit a95min that helps to ascertain whether or not a distribution has sufficiently well sampled psv and therefore geomagnetic field behaviour applying these criteria is indispensable for studies of geomagnetic behaviour or for studies aiming at using tk03 gad for inclination error correction through the elongation inclination e i method for palaeomagnetic studies aimed at geological reconstructions they form helpful guidelines and increase the confidence in the rocks having faithfully recorded the field an analysis of published eastern mediterranean data shows that the vast majority of studies do not conform to the van der voo criteria in particular with respect to n and a95 we have provided criteria that are on the one hand more lenient lower n may still provide relevant information and on the other hand more strict for high n the criterion of a95 16 should be adapted to a requirement of lower a95 e g a95 80

paleomagnetism of a lateritic paleoweathering horizon and overlying paleoproterozoic red beds from south africa implications for the kaapvaal apparent polar wander path and a confirmation of atmospheric oxygen enrichment the olifantshoek group in southern africa contains paleoproterozoic red beds that are exceptionally well preserved lying unconformably atop a regionally extensive lateritic paleoweathering profile we studied the basal unit of this succession known as the gamagara or mapedi formation and the lateritized substrate so called drakenstein or wolhaarkop paleosol on which it developed two ancient magnetic components are observed one int usually with a distributed unblocking spectrum between 300 and 600 c but occasionally persisting to 675 c is directed shallowly southward or northward a mesoscale fold test at south sishen mine indicates that this component was acquired during deformation similarity of the direction to previous results suggests that it was acquired at 1240 ma during early namaqua orogenesis combining our int results with existing data from the namaqua eastern zone nez we calculate the nez pole at 44 9 n 021 5 e k 23 2 a 95 12 8 q 5 the most stable component from our data set hig always persisting as a nonzero endpoint to demagnetization at 665 680 c is observed in 32 samples from south sishen and beeshoek mines directed moderately east downward sishen or west upward beeshoek this component predates the mesoscale fold at sishen more importantly a conglomerate test at beeshoek indicates that hig was acquired prior to paleoproterozoic deposition of the gamagara mapedi formation the concordance between directions from the paleoweathering zone and immediately overlying red beds indicates that hig is a primary magnetic remanence for the basal gamagara mapedi bgm formation the dual polarity bgm paleomagnetic pole 02 2 n 081 9 e dp 7 2 dm 11 5 q 6 lies neatly between previous kaapvaal poles with ages of 2220 ongeluk lavas and 2060 ma bushveld complex our data thus support recent correlations of the gamagara mapedi formation with pre bushveld sediments of the pretoria group a pre bushveld age for bgm is also consistent with its substantial distance from a new albeit less reliable paleomagnetic pole from the 1930 ma hartley lavas higher within the olifantshoek succession 12 5 n 332 8 e k 18 6 a95 16 0 q 3 our conglomerate test at beeshoek confirms previous allegations that the intense hematitization observed in the drakenstein wolhaarkop paleosol occurred during paleoproterozoic weathering under a highly oxygenated atmosphere

phanerozoic evolution of the inner mongolia daxinganling orogenic belt in north china constraints from geochronology of ophiolites and associated formations

phanerozoic granitoids in the central and eastern parts of central asia and their tectonic significance abstract the widespread occurrence of voluminous granitoids is a typical characteristic of the central asian orogenic belt caob in the central and eastern parts of central asia the granitoids occupy a total area more than 8 million km2 with three major area peaks at cambro ordovician carboniferous permian and jurassic six zircon age peaks at ca 500 430 370 330 300 290 260 210 170 and 145 110 ma the early paleozoic granitoids 540 440 ma with age peak at ca 500 ma mainly occur in the northwestern caob and are of calc alkaline i type they probably formed in a subduction setting 500 480 ma within the paleo asian ocean pao and subsequent microcontinental collision ca 460 ma the middle paleozoic granitoids 430 370 ma predominately occur in the nw and southern caob and are characterized by a high k calc alkaline affinity suggesting an accretionary and or a collisional setting the late paleozoic 350 260 ma granitoids are widespread in the caob and formed in variable tectonic settings within an intra continental regime or active continental margins in the pao and in the evolving mongol okhotsk ocean moo carboniferous granitoids 350 300 ma in the northern and northwestern caob exhibit a type alkaline features and formed in a post accretionary settings whereas granitoids in the southern caob show i type calc alkaline features and were generated in an arc setting permian granitoids 290 270 ma are predominantly of i a a type with alkaline signatures associated with coeval mafic magmatism and suggesting a post collisional or intraplate setting contemporaneous with a large igneous province lip in the tarim craton some 270 250 ma calc alkaline granitoids also occur in the southernmost caob combined with 250 245 ma high sr y granitoids these rocks reflect final closure of the pao during 270 250 ma early mesozoic mainly triassic granitoids occur mainly in the eastern caob or eastern central asia the early phase granitoids 250 230 ma are of i and s types whereas the mid and late phase granitoids ca 230 190 ma are of a type and transitional i a type or highly fractionated i type all these granitoids occur in variable settings intraplate post orogenic and continental arc related to three tectonics regimes namely the paleo asian ocean pao the mongol okhotsk ocean moo and the paleo pacific ocean ppo late mesozoic granitoids mainly occur in eastern central asia and were emplaced during 6 major magmatic events at 190 180 180 165 165 145 145 135 135 100 and 100 60 ma the 190 165 ma granitoids are of i type calc alkaline high k calc alkaline and evolved along active margins related to the mongol okhotsk and paleo pacific ocean domains the 145 120 ma granitoids are highly fractionated i transitional i a or a types with high k calc alkaline shoshonitic signatures the magmatic evolution from the late jurassic to early cretaceous coincided with a tectonic transition from contractional thickened crust to extensional thinning the 120 65 ma granitoid magmatism displays a southeastward younging trend suggesting a roll back of the paleo pacific oceanic plate the granitoids in the caob of eastern central asia show variable whole rock nd and hf in zircon isotopic compositions and most have juvenile signatures in some regions e g altai junggar and great xing an the volume of juvenile and slightly juvenile crust

an algorithm for u pb isotope dilution data reduction and uncertainty propagation this is the publisher s version also available electronically from http onlinelibrary wiley com