prolonged magmatism juvenile nature and tectonic evolution of the chinese altai nw china evidence from zircon u pb and hf isotopic study of paleozoic granitoids abstract paleozoic granitoid magmatism played an important role in the tectonic evolution of the chinese altai and zircon u pb and hf isotopic compositions have been determined for samples from eleven granitic plutons batholiths the jiadengyu gneissic granitic pluton yielded a zircon u pb age of 479 ma and thus it does not represent precambrian basement as suggested previously our results and published data demonstrate that voluminous granitoids were continuously emplaced over more than 30 area of the chinese altai during the period from 447 ma to 368 ma with a climax at ca 400 ma ages for zircon overgrowth rims demonstrate additional thermal events at ca 360 and 280 ma respectively positive e hf t values 0 to 9 of normal magmatic zircons suggest that the granitoid magmas were derived from juvenile sources xenocrystic zircon cores are 543 421 ma old and also give positive e hf t values 2 5 to 12 suggesting their origin as early crystallized minerals in the magma chambers or as inherited cores from newly accreted meterials the strong magmatism at ca 400 ma significantly changed the hf isotopic composition of the magma source by substantial input of juvenile material in a relatively short period geophysical geological and geochemical data support that ridge subduction was a possible mechanism for the strong magmatism ca 400 ma and the above mentioned change of hf isotopic composition in the magma source

tomographic upper mantle velocity structure beneath the iranian plateau the iranian plateau is one of the most structurally complex and tectonically inhomogeneous regions in the world in this study we analyze pn arrival times from regional seismicity in order to resolve lateral velocity variations within the uppermost mantle under the iranian plateau more than 48 000 pn first arrival times selected from the ehb catalog were used with epicentral distances of 200 to 1600 km we used regularized isotropic and anisotropic damped least squares inversion to image lateral velocity variations in the upper mantle our velocity model with high lateral resolution shows positive anomalies in the zagros mountain belt with a distinct transition approximately along the main zagros thrust to the lower mantle velocity zone of central iran anomalously low velocities are observed predominantly beneath nw iran and eastern turkey suggesting a zone of relatively weak mantle low velocity region under the damavand volcano reveals the hot upper mantle beneath the central alborz mountains

volcanic record of the subduction of an active spreading ridge taitao peninsula southern chile during the pliocene the taitao peninsula was the locus of the subduction of the chile active spreading ridge beneath the south american margin new field data allow us to distinguish within the taitao ophiolite a genuine ophiolitic body of undetermined age and two volcanic and volcaniclastic units one unit shows evidence for deposition in a shallow water environment and it unconformably overlies the chilean continental basement its established pliocene age demonstrates that it was deposited during the subduction of the chile ridge lavas from both units include enriched mid oceanic ridge basalts morbs together with nb depleted basalts andesites and dacites la nb ratios vary randomly from 1 to 4 in both units and are positively correlated with sio 2 content these chemical characteristics are consistent with upper crustal contamination of morb type basalts by the chilean crust as already suggested from isotopic data we consider these volcanic suites to be the result of eruptions of morb magmas that originated from the downgoing shallowly buried active spreading center and were contaminated during their rise through the chilean continental basement

zircon u pb and hf isotopic study of gneissic rocks from the chinese altai progressive accretionary history in the early to middle palaeozoic abstract gneissic rocks in the chinese altai mountains have been interpreted as either paleozoic metasedimentary rocks or precambrian basement this study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a ne sw traverse in the northwestern chinese altai petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from i type granites formed in a subduction environment three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 ma some give neoproterozoic ages and a few yield discordant paleoproterozoic to archean ages zircon hf isotopic compositions indicate that both juvenile mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived in contrast zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids and define single populations for each sample with mean ages between 380 and 453 ma the general absence of precambrian inheritance and positive zircon hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas our data can be interpreted in terms of a progressive accretionary history in early to middle palaeozoic times and the chinese altai may possibly represent a magmatic arc built on a continental margin dominated by neoproterozoic rocks

thermochronological constraints on the late paleozoic tectonic evolution of the southern chinese altai abstract the chinese altai as an accretionary orogen developing from the cambrian to carboniferous was modified by permian deformation metamorphism and magmatism in response to the collision with the east junggar the tectonic processes of the collision and the timing of related deformation and metamorphism are still enigmatic here we present new 40 ar 39 ar dating results for granitic gneisses and amphibolites exposed in the qiongkuer domain in two areas alahake and fuyun of the southern chinese altai the amphiboles from both aalaheke and fuyun areas yield consistent 40 ar 39 ar plateau ages at 265 9 1 7 ma and 270 1 3 1 ma in contrast the biotites from two areas show distinct 40 ar 39 ar ages of 232 0 2 1 ma and 226 8 1 7 ma for the alahake area and 245 1 1 5 ma and 264 5 2 2 ma for the fuyun area respectively given that 40 ar 39 ar ages are younger than the permian high temperature metamorphism at 299 277 ma as constrained by metamorphic zircons in the qiongkuer domain we interpret these 40 ar 39 ar ages to record the cooling history of two areas compatible amphibole ages in both areas indicate a similar exhumation age along the qiongkuer domain cooling through 550 c at 270 265 ma which may have been associated with the development of the sinistral erqis shear zone during the collision between the chinese altai and the east junggar the subsequent exhumation processes were variable in different areas of the qiongkuer domain as showed by the distinct biotite ages which may indicate along strike variation of cooling processes from 550 c to 300 c in the qiongkuer domain

petrogenesis and magmatic hydrothermal evolution time limitation of kelumute no 112 pegmatite in altay northwestern china evidence from zircon upb and hf isotopes abstract granitic pegmatites and associated rare metal deposits unique features in the altay orogen are located in a key tectonic position of the southern central asian orogenic belt caob and document the tectonic evolution of the paleo asian ocean the kelumute no 112 pegmatite which intruded into the jideke two mica granites hosts abundant rare metal e g li be nb ta ore deposits and ranks only second to the koktokay no 3 pegmatite in both size and reserves to explore the evolution time limitation of magmatic magmatic hydrothermal and hydrothermal stages in the pegmatite magma system the tectonic setting and the genetic relationship between pegmatites and granites this study presents zircon u pb and hf isotopic compositions of the kelumute no 112 pegmatite and the wall rocks two mica granite and biotite granite as determined by la icpms and la mc icpms the weighted mean 206 pb 238 u ages of the internal textural zones of the pegmatite including zones i ii iii v and vi are 238 3 2 0 ma 233 5 3 7 ma 188 3 1 7 ma 218 8 1 9 ma and 210 7 1 6 ma respectively wall rocks of two mica granite and biotite granite are dated at 445 6 4 3 ma and 455 6 5 4 ma respectively zircons from the kelumute no 112 pegmatite have lower positive e hf t values 0 03 to 2 35 with t dm model ages of 1112 1225 ma wall rocks show similar zircon e hf t values 1 41 to 4 13 and t dm model ages 1172 to 1515 ma however three xenocrystic zircons from the granites are characterized by larger negative ehf t values 5 85 to 9 83 and older t dm model ages 1839 to 2090 ma thus the following conclusions can be drawn 1 the kelumute no 112 pegmatite and its wall rocks jideke two mica granite and biotite granite have no genetic relationship as indicated by the large gaps between their formation ages however they did originate from a common source composed of ancient crust and mantle derived materials under two different tectonic settings 2 the magmatic magmatic hydrothermal transition and hydrothermal stages of the no 112 pegmatite magma lasted for 5 ma 23 ma and 22 ma respectively and 3 the no 112 pegmatite magma was most likely formed in a post collision tectonic setting indicating that block amalgamation and collisional orogeny of the caob continued into the triassic

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

geodynamic significance of s type granites in circum pacific orogens in phanerozoic circum pacific orogenic belts most post collisional s type granites and associated high temperature low pressure metamorphic complexes formed during early arc extension the granites are part of a tripartite association consisting of 1 inboard s type granite 2 outboard oceanic arc and 3 intervening turbidite filled backarc basin s type granites herald the formation of new outboard oceanic arc and extensional backarc systems but thickening of a preexisting sediment dominated back arc basin is a prerequisite for their generation in these environments s type plutonism is triggered by renewal of arc magmatism following thickening when hot basaltic magmas are intruded into the thickened backarc crust once slab retreat is reestablished with ongoing extension during retreat the crust becomes progressively thinned the sedimentary contribution is diminished and the granites lose their s type character such tripartite associations involving s type granite are probably diagnostic of repeated slab retreat episodes and the jurassic u s cordillera might be an example

response of winter moisture circulation to the india burma trough and its modulation by the south asian waveguide abstractthe response of moisture circulation to the daily evolution of the india burma trough ibt and the modulation of disturbances along the south asian waveguide are analyzed to seek a potential precursor of winter precipitation over south china daily observational precipitation and reanalysis data from era interim during 1979 2012 are employed it is found that moisture circulation in response to the ibt is part of the zonally oriented wave trains along the south asian waveguide but it persists longer and migrates farther eastward than other lobes cyclonic moisture transport enhances the moisture supply to south china as a strong ibt develops and shifts eastward abruptly after the peak of ibt with enhanced precipitation shifting from southwest to southeast china this response is a joint effect of synoptic intraseasonal and interannual components that show similar wave train structures whereas slight differences still occur the synoptic component shows a shorter wavelength more southerly pa

modulation of south asian jet wave train on the extreme winter precipitation over southeast china comparison between 2015 16 and 2018 19 abstracttwo extremely wet winters in 2015 16 and 2018 19 over southeast china are compared in this study south to north discrepancies appear in the spatial distribution of precipitation with anom

the 390 ma high t metamorphic event in the chinese altai a consequence of ridge subduction high grade rocks occur in the chinese altai but the timing of metamorphism is poorly constrained which hinders our understanding of the thermo tectonic history of the region representative high grade samples from the sillimanite zone extending from hanas to fuyun were selected for zircon u pb dating and temperature estimation la icp ms analyses of zircon overgrowth rims and recrystallized domains give consistent ages of 390 ma which is interpreted to record a regional metamorphic event temperature t estimations using the amphibole plagioclase quartz amp pl qtz and garnet biotite gb geothermometers give relatively high temperatures ranging from 650 to 700 c the zircon metamorphic rims yield temperature estimates of 720 c by using the ti in zircon thermometer these data suggest that a high temperature metamorphic event took place in the chinese altai in the middle devonian and may imply a tectonic environment involving an unusually elevated heat flux from a deep seated source our data support possible ridge subduction around 390 ma that caused upwelling of the hot asthenosphere and triggered the high t metamorphism this model can also account for coeval volcanic activity with a range of geochemical characteristics diverse mafic intrusions and extensive hydrothermal mineralization in the altai orogen

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

continental growth of northwest china the northwest corner of china is the most interior part of central asia and includes parts of the siberian tarim and kazakhstan plates where the junggar and tarim basins are separated by the east west trending tianshan range a preliminary terrane map divides the area into thirteen separate areas which are classified into four types l continental 2 oceanic crust 3 island arc 4 composite the boundaries for these terranes are faults that have been previously defined either by geologic mapping or holocene activity passive consolidation of the southern margin of paleo asia is marked by accretion and subduction of the paleo tethys oceanic basins and by development of volcanic arcs paleomagnetic data indicate that the major plates and associated smaller terranes did not reach final consolidation until the permian or later the stratigraphic record reveals development of intracontinental basins in the late carboniferous followed by the pan asian thermal event that gave rise to widespread intrusion of a type granites of late paleozoic age the frontal collision of india along the southern border of asia in the paleocene reactivated nearly all of the older major strike slip and thrust faults formed during the late paleozoic consolidation of paleo asia the complex nature of the continental growth of central asia has produced and destroyed many varieties of sutures and reconstruction of the original plate and terrane configurations therefore is enigmatic

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

late devonian early permian a type granites in the southern altay range northwest china petrogenesis and implications for tectonic setting of a 2 type granites abstract the altay range is an important part of the central asian orogenic belt caob that contains a type granites that have been attributed to a post collisional setting during the late carboniferous permian however our new la icp ms zircon u pb age data demonstrates that there were two episodes of a type granite magmatism in the southern altay range a late carboniferous to early permian 308 291 ma suite does occur in the vicinity of qiakuerte but a distinct late devonian 382 367 ma suite is present in the kouan area the early kouan a type granites are mainly composed of alkali feldspar granites which are approximately synchronous with adakites boninites high ti basalts picrites ophiolitic rocks and high temperature low pressure metamorphic rocks whereas the late qiakuerte a type granites mainly consist of arfvedsonite and aegirine bearing granites which are approximately coeval with some mafic ultramafic rocks in the southern altay range a type granites are commonly classified as a1 and a2 sub types which are considered to be generated in anorogenic rift or plume related or post collisional settings respectively both suites of the southern altay range are geochemically similar to typical a2 type granites e g high k2o na2o feo mgo and ga al and y nb values and low cao ba sr and eu contents the kouan a type granites have relatively low la yb n 2 7 5 9 high end t 6 7 to 7 7 and nb la 0 59 1 67 and variable ehf t 5 0 to 14 1 values whereas the qiakuerte a type granites have comparatively high la yb n 4 2 9 2 low end t 5 3 to 6 0 and nb la 0 33 0 74 and variable ehf t 10 0 to 18 7 values the early kouan a type granites may have been generated by partial melting of a mafic source containing more depleted mantle derived components than the late qiakuerte a type granites we suggest that the late carboniferous to early permian qiakuerte granites were formed in a post collisional extensional setting as is typical of a2 type granites however the late devonian kouan a type granites were more plausibly generated in an extensional setting as a result of slab window caused by a ridge subduction in this case the upwelling of asthenosphere through the slab window provided the source of parental magmas or the heat for the generation of devonian magmas therefore our results suggest that a2 type granites can also form in a ridge subduction related extensional setting

geochemical and isotopic studies of the sedimentary and granitic rocks of the altai orogen of northwest china and their tectonic implications the altai orogen northwest china represents the southwestern margin of the central asian orogenic belt geochemical and nd sr isotope analyses were carried out on the palaeozoic sedimentary and granitic rocks in order to trace their sources and to evaluate the pattern of continental growth of the orogen nd isotopic data for both the granites and sediments suggest a significant proportion of middle proterozoic crust beneath the altai orogen however addition of juvenile material arc back arc oceanic crust during palaeozoic times is also significant trace elements and isotopic data of sediments suggest their sources were immature they represent mixtures between a palaeozoic juvenile component and an evolved continental crust the early palaeozoic sediments show e nd t 3 4 to 5 0 t dm 1 5 1 8 ga and i sr 0 710 0 712 they represent a passive margin setting with a predominance of evolved crustal material in the source the devonian sequences however might have been deposited in a back arc basin setting produced by subduction of the junggar oceanic crust along the irtysh fault a significant addition of arc material into the sedimentary basin is responsible for the highly variable e nd values 6 to 0 and i sr 0 711 0 706 the carboniferous rocks were also deposited in a back arc basin setting but with predominantly arc material in the source as suggested by an abrupt increase in e nd t 6 to 3 and decrease in i sr 0 7045 0 7051 voluminous syn orogenic granitoids have e nd t 2 1 to 4 3 i sr 0 705 0 714 and t dm 0 7 1 6 ga they were not derived by melting of local metasedimentary rocks as suggested by previous workers but by melting of a more juvenile source at depth post orogenic granites have higher e nd t 4 4 than the syn orogenic granitoids indicating their derivation from a deeper crustal level where juvenile crust may predominate

the western central asian orogenic belt a window to accretionary orogenesis and continental growth abstract the architecture of accretionary orogens is a key to understand continental growth here we present an overview of the orogenic components and their amalgamation in the western central asian orogenic belt caob the caob records the convergence and interactions among various types of orogenic components including the japan type mariana type and alaska aleutian type arc systems as well as the active marginal sequences of the siberia craton which incorporated wide accretionary complexes and accreted arcs and terranes during construction of the caob the kazakhstan arc chain was characterized by multiple subduction whereas the northern fringe of the tarim craton remained mostly as a passive margin the multiple convergence and accretions among these various orogenic components generated huge orogenic collages in the late paleozoic and even in the early triassic involving parallel amalgamation circum microcontinent amalgamation and oroclinal bending the preservation of trapped basins played a significant role in orogenesis with some parts of the oceanic plate being subducted and others behaving as rigid units the orogenesis in the caob was long lived lasting for more than 800 m y involving multiple subduction and long continuous accretion and featuring the complexity of accretionary orogenesis and continent growth

northwestern junggar basin xiemisitai mountains china a geochemical and geochronological approach abstract we report sims u pb zircon elemental and nd sr pb isotopic data for the volcanic rocks and their subvolcanic units from the xiemisitai mountains in the west junggar region xinjiang china aiming to determine their ages source regions and tectonic setting zircon u pb dating results of the volcanic rocks 422 5 1 9 ma 411 2 2 9 ma indicate that the volcanic strata occurred in the xiemisitai mountains at late silurian early devonian time rather than middle devonian as suggested previously they are probably the eastern extension of the early paleozoic cambrian silurian boshchekul chingiz volcanic arc of east kazakhstan in china the xiemisitai volcanic rocks include andesite rhyolite and their pyroclastic equivalents the subvolcanic units are felsite and granite porphyry andesite is moderately lree enriched with a marked negative nb anomaly and th yb enrichment rhyolite felsite and granite porphyry are enriched in lree and th and depleted nb the initial sr isotope values of the xiemisitai volcanic rocks and their subvolcanic units range from 0 702294 to 0 704456 e nd 420 ma from 0 19 to 1 88 with nd model ages ranging from 600 to 803 ma initial pb isotope ratios 206 pb 204 pb are 17 77 17 96 207 pb 204 pb are 15 49 15 54 and 208 pb 204 pb are 37 56 37 80 these features suggest that the xiemisitai volcanic rocks and their subvolcanic units derived from a mantle wedge significant mixed by subducted material emi in a subduction zone they also indicate significant involvement of neoproterozoic primitive crust in the formation of the xiemisitai magmatic arc these rocks are associated with a late silurian early devonian southward subduction of the oceanic lithosphere in the northern west junggar region this gives rise to an ew trending boshchekul chingiz volcanic arc and associated metallogenic belt in the northern west junggar region and adjacent kazakhstan

improvements of precision and accuracy in in situ hf isotope microanalysis of zircon using the laser ablation mc icpms technique abstract we have developed a new analytical technique for precise and accurate in situ hf isotope ratio measurements for zircons by means of laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icpms newly designed sample cell and n 2 mixing technique provided higher elemental sensitivity with smoother signal intensity profiles in order to improve the accuracy of the hf isotope ratio analysis previously reported correction methods for isobaric interferences on 176 hf by 176 yb and 176 lu were rigorously evaluated and we found that the use of independent mass bias factors for hf and yb in the isobaric interference correction resulted in more reliable hf isotopic data in order to test the reliability of the hf isotopic data from 35 m diameter ablation pits that are smaller than the typical size of most zircon grains lu hf isotopes for three zircons harvard 91500 antarctic zircon pma7 and acasta zircon ay199 were measured the present 176 hf 177 hf isotope ratio of 0 282321 46 2 s d and initial 176 hf 177 hf isotope ratio of 0 282315 47 2 s d were obtained for zircon standard 91500 the resulting present 176 hf 177 hf isotope ratio shows an excellent agreement with the previously reported data our in situ isotopic data revealed that the lu hf ratio varied significantly within the 91500 grain 176 lu 177 hf 0 000130 0 000345 suggesting the existence of slight isotopic heterogeneity in present 176 hf 177 hf approximately 15 ppm for antarctic zircon pma7 despite the smaller size of the single grain 50 100 m wide 80 300 m long and the presence of various mineral inclusions resulting analytical precision for the initial 176 hf 177 hf ratio was 128 ppm 0 281208 36 2 s d for acasta zircon ay199 despite the high yb hf 0 05 and lu hf 0 01 isotope ratios with the early archean crystallization age 3 74 ga resulting analytical precision for the initial 176 hf 177 hf ratio was 187 ppm 0 280160 52 2 s d these results demonstrate clearly that in situ hf isotope ratio microanalysis developed here has the potential to become a significant tool for zircon lu hf isotopic study

modulation of the interannual variation of the india burma trough on the winter moisture supply over southwest china anomalous moisture circulation associated with the interannual variation of the india burma trough was investigated to examine how the trough affects the moisture supply to southwest china in winter when the india burma trough is strong abnormal moisture is transported to southwest china mainly via the southern boundary in the 750 650 hpa layer instead of via the western boundary in contrast to the climatological situation the abnormal moisture convergence is constrained in a thin layer along the windward side of the tibetan plateau the moisture circulation response to the variation of the india burma trough shows great baroclinicity over the bay of bengal bob northwesterly transport behind and southwesterly transport ahead of the trough appear only between 850 and 650 hpa with anticyclonic moisture circulation underneath and cyclonic moisture circulation on top beyond the bob the moisture circulation response can be traced upstream with abnormal anticyclonic cyclonic moisture circulations over the mediterranean sea and arabian sea red sea above 850 hpa and downstream with anticyclonic moisture circulation over the philippine sea near the surface the activity of the india burma trough is not a local phenomenon but a part of the south asian jet wave trains and is modulated by the enso via the philippine sea anticyclone further investigation of the separate role of wind and moisture disturbances shows that the abnormal moisture flux is dominated by the wind disturbance as is the abnormal moisture divergence in the lower level while that in the upper level is dominated by both the wind and moisture disturbances

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

an evolving tectonic environment of late carboniferous to early permian granitic plutons in the chinese altai and eastern junggar terranes central asian orogenic belt nw china abstract the central asian orogenic belt caob represents one of the most important sites of juvenile crustal growth during the phanerozoic located in the central part of the caob the chinese altai and eastern junggar terranes record the collisional processes between the peri siberian and kazakhstan orogenic systems however the precise timing of collision between the two terranes remains controversial the wukuli and kadelat plutons in the chinese altai belt are dated at 305 and 280 ma respectively whereas the aketas pluton in the eastern junggar terrane is dated at 308 ma granites from the wukuli and kadelat plutons are strongly peraluminous a cnk 1 1 and are characterized by low al 2 o 3 na 2 o mno mgo cao and heavy rare earth element hree contents but with high sio 2 k 2 o and rb contents as well as high rb sr ratios granites from the wukuli pluton have low e nd t and e hf t values of 3 7 to 3 4 and 9 7 to 4 9 whereas those from the kadelat pluton have values of 3 6 to 3 4 and 8 0 to 2 6 these features suggest s type affinity for the wukuli and kadelat plutons with magma derivation through partial melting of mesoproterozoic metasediments the aketas pluton is composed of weakly peraluminous quartz monzonites that have a cnk values ranging from 0 92 to 1 08 with high na 2 o sr and sr y and low y yb nb and ta these rocks display positive e nd t 4 8 to 6 4 and e hf t 9 7 to 14 6 values and low initial 87 sr 86 sr ratios 0 703357 0 703868 similar to modern adakites suggesting that the quartz monzonites were derived from the partial melting of lower crustal material the geochemical characteristics suggest that the aketas pluton was formed in a subduction related setting the wukuli pluton in a syn collisional setting and the kadelat pluton in the subsequent post orogenic strike slip related setting in combination with data from other granitoids in these two terranes the aketas pluton represents the youngest record of subduction related environments suggesting that the final collision between the chinese altai and eastern junggar terranes might have occurred between 308 and 304 ma

late silurian early devonian adakitic granodiorite a type and i type granites in nw junggar nw china partial melting of mafic lower crust and implications for slab roll back abstract late silurian early devonian magmatism of the nw junggar region in the central asian orogenic belt provides a critical geological record that is important for unraveling regional tectonic history and constraining geodynamic processes in this study we report results of zircon u pb ages and systematic geochemical data for late silurian early devonian largely granitic rocks in nw junggar aiming to constrain their emplacement ages origin and geodynamic significance the magmatism consists of a variety of mafic to felsic intrusions and volcanic rocks e g adakitic granodiorite k feldspar granite syenitic granite gabbro and rhyrolite u pb zircon ages suggest that the granitoids and gabbros were emplaced in the late silurian early devonian 420 405 ma adakitic granodiorites are calc alkaline characterized by high sr 407 532 ppm low y 12 2 14 7 ppm yb 1 53 1 77 ppm cr mostly

late paleozoic faults of the altai region central asia tectonic pattern and model of formation abstract the present kinematic and dynamic analysis of large scale strike slip faults which enabled the formation of a collage of altai terranes as a result of two collisional events the late devonian early carboniferous collision of the gondwana derived altai mongolian terrane and the siberian continent resulted in the formation of the charysh terekta system of dextral strike slip faults and later the kurai and kuznetsk teletsk bashkauss sinistral strike slip faults the late carboniferous permian collision of the siberian and kazakhstan continents resulted in the formation of the chara irtysh and north east sinistral strike slip zones the age of deformation of both collisional events becomes younger toward the inner areas of the siberian continent in the same direction the amount of displacement of strike slip faulting decreases from several thousand to several hundred kilometers the width of the late paleozoic zone of deformation reaches 1500 km these events deformed the accretion collision continental margins and their primary paleogeographic pattern

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

geochronology of the karadere basement nw turkey and implications for the geological evolution of the istanbul zone earlier geological work in the istanbul zone western pontide tectonic belt has revealed the presence of extensive basement outcrops exposed underneath palaeozoic and mesozoic to tertiary cover sequences the basement of suspected neoproterozoic age plays an important role in understanding the crustal accretion process in nw turkey we report the first results of a detailed pb pb and u pb zircon study complemented by nd sr whole rock and mineral data from basement rocks exposed in the karadere valley safranbolu area five samples were selected for this study comprising three metagranitoids and two metasediments zircon geochronology indicates that the metagranitoids were formed during late proterozoic pan african magmatic events between 590 and 560 ma the rocks are of tonalitic and granitic composition and have low nb y ratios and ti contents consistent with those of arc rocks a continental arc setting is supported by their sr and nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis the metasediments can clearly be distinguished from the metagranitoids by their higher 87sr 86sr ratios and lower end values at 580 ma which supports the suggestion that the arc was underlain by mature continental crust zircons from the metasediments yield a range of pb pb ages between 1 860 and 710 ma thirty per cent of them fall between 890 and 710 ma possibly suggesting a derivation from gondwana afro arabian regions a sm nd garnet whole rock analysis obtained on a metagranite gives an age of 559 8 ma which either reflects pre metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high temperature metamorphic event uplift and cooling of the basement is further constrained by rb sr biotite ages of 548 545 ma these lower cambrian mineral ages demonstrate that the istanbul zone was not thermally reactivated during the hercynian cimmerian or alpine orogeny in contrast to its neighbouring tectonic zones confirming its role as a suspect terrane in the modern western pontide tectonic belt

summer atmospheric bridging between europe and east asia influences on drought and wetness on the tibetan plateau abstract based on the era 40 reanalysis data dryness and wetness over the tibetan plateau are categorized according to the monthly standardized precipitation index the atmospheric features associated with severe and extreme dryness and wetness reveal two cross eurasia wave trains the scandinavia east asia wave train and the mediterranean east asia wave train severe and extreme dryness is associated with an anomalous cyclone over south and southeast asia which directs the moisture supply from the arabian sea the bay of bengal and the south china sea directly eastward towards the western pacific thus bypassing the tibetan plateau this cyclone anomaly constitutes part of the scandinavia east asia wave train which is sustained by the divergence and convergence of the anomalous transient eddy heat transport associated with a more southwest northeast oriented north atlantic storm track and a northward shift of the polar front jet in the north atlantic in contrast severe and extreme wetness over the tibetan plateau is associated with a more zonally elongated north atlantic storm track wave trains excited from there have a high probability to reach the mediterranean region and to propagate eastward following the subtropical westerly jet this mediterranean east asia wave train generates anticyclonic anomalies around the tibetan plateau and east china which bring more moisture supply from the arabian sea the south china sea and the western pacific towards the tibetan plateau and enhance the moisture convergence there this paper demonstrates how atmospheric bridging processes affect regional climate variability under present day climatic conditions which are also relevant for understanding past climates

late paleozoic strike slip shear zones in eastern central asia nw china new structural and geochronological data 1 new structural studies and 40ar 39ar dating in northwest china provide information about late paleozoic strike slip motions subsequent to accretional events which built eastern central asia during the paleozoic two principal areas were affected by these large transcurrent motions first in the tianshan range main east west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism associated biotites give ages ranging from 290 ma to 245 ma the earlier n110 shearing occurred in western tianshan while the last one dextral in whole tianshan occurred 250 245 myr ago second in the chinese altay region several nw se shear zones structured the area the main motion is sinistral and occurred along the erqishi zone at 280 290 ma it is followed by a complex succession of dextral and sinistral shearing episodes leading to the northwestward structuring dated at 245 ma of a metamorphic zone that was folded during a compressive event

quasi 4 yr coupling between el nino southern oscillation and water vapor transport over east asia wnp abstractthe summer moisture circulation anomaly over east asia and the western north pacific wnp couples well with the el nino southern oscillation enso in a quasi 4 yr period the moisture circulation is dominated by two well separated modes the first mode exhibits an anticyclonic cyclonic moisture circulation over tropical subtropical east asia wnp with an easterly westerly transport over the tropical wnp indian ocean the second mode displays an alternating pattern with an anticyclonic cyclonic moisture circulation over the subtropical wnp layered between two cyclonic anticyclonic circulations both modes couple well with the enso signal during its quasi 4 yr cycle within the cycle in the summer of a developing warm episode the positive phase of the second mode plays a key role while in the transitional summer between a decaying warm episode and a developing cool episode the positive phase of the first mode tends to take effect in the summer of a developing cool episode the negative

high and low latitude types of the downstream influences of the north atlantic oscillation using reanalysis data we find that the downstream propagating quasi stationary rossby wave train associated with the north atlantic oscillation nao generally propagates along a high low latitude pathway during warm cold el nino southern oscillation enso boreal winters consistent with the different propagation directions of the nao related downstream wave train during the warm cold enso winters the nao is associated with significant 300 hpa geopotential height anomalies over eastern siberia the arabian sea the east coast of asia at around 40 n and the north pacific and the near surface air temperature perturbations associated with the nao over the high latitudes of asia are relatively strong weak based on these differences we argue that the nao has two distinct types of downstream influence a high latitude type and a low latitude type furthermore we argue that the two types of nao s downstream influence are modulated by the intensity of the subtropical potential vorticity pv meridional gradient over africa when this gradient is weak strong as in the warm cold enso winters the nao s downstream influence tends to be of the high low latitude type these results are further supported by analysis of intraseasonal nao events we separate nao events into two categories in terms of the intensity of the subtropical pv gradient over africa composites of the nao events accompanied by a weak strong subtropical pv gradient show that the nao related downstream wave train tends to propagate along a high low latitude pathway

formation of the maturin foreland basin eastern venezuela thrust sheet loading or subduction dynamic topography 1 the maturin basin in eastern venezuela is considered a good example of a peripheral foreland basin earthquake and tomographic data indicate that eastern venezuela is affected by the oblique subduction of the south american plate underneath the caribbean plate new forward flexural isostatic modeling of eastern venezuela has been carried out in order to determine whether the maturin basin was generated purely by thrust sheet loading from the serrania and monagas foreland thrust belts a sequence of forward models from middle miocene to present was generated for 3 profiles across the serrania del interior thrust belt the monagas foreland thrust belt and the maturin foreland basin the predictions of these models are constrained using seismic reflection and well data the flexural isostatic modeling shows that thrust sheet loading associated with the serrania del interior and monagas foreland thrust belts is insufficient to generate the observed subsidence within the maturin basin dynamic fluid flow modeling of subduction related dynamic topography of eastern venezuela has been used to investigate the influence of south american plate subduction on the generation of the accommodation space observed in the maturin basin fluid flow modeling of subduction related dynamic topography suggests that the subduction of the south american lithospheric mantle caused downward deflection of the south american crust affecting the maturin basin and the serrania thrust belt this modeling suggests that the maturin basin subsidence has two components 55 related to thrust sheet loading and 45 driven by continental subduction

adakites without slab melting high pressure differentiation of island arc magma mindanao the philippines abstract new geochemical data for pleistocene magmatic rocks from the surigao peninsula eastern mindanao the philippines demonstrate typical adakitic traits including elevation of sr y and depletion of the heavy rare earth elements 87sr 86sr and 143nd 144nd ratios of the adakites do not support melting of the subducted philippine sea plate but resemble pliocene arc lavas generated in the same subduction zone excepting the heavy rare earth elements the adakites and arc lavas also possess similar ratios of incompatible elements suggesting that the adakites were ultimately derived from melting of the mantle wedge the wide range of sio2 in the adakites and its strong correlation with trace element concentrations and ratios indicate two possible mechanisms for generating the adakitic signature 1 adakitic melt was produced from basaltic arc magma by fractional crystallisation of a garnet bearing assemblage 2 solidified basaltic rock containing garnet melted to yield adakitic magma in either case the basaltic precursor was generated from fluid modified mantle then differentiated within the garnet stability field in surigao this requires differentiation within mantle the surigao example suggests that any subduction zone has the potential to produce adakitic magma if basalt crystallises at sufficient depth this has important implications for the geodynamics of modern and ancient subduction zones that have generated similar rocks

carboniferous mantle derived felsic intrusion in the chinese altai nw china implications for geodynamic change of the accretionary orogenic belt abstract this paper reports whole rock sr nd and zircon u pb and hf isotopic compositions as well as major and trace element data for the granodiorites and their mafic microgranular enclaves mmes in the tuokesalei area northwestern chinese altai the granodiorites are characterized by peraluminous compositions a cnk 1 01 1 45 with relatively high sio 2 64 4 to 70 9 wt and low mgo 0 75 to 1 97 wt contents these rocks possess low total rare earth element ree contents 67 187 ppm with weakly negative eu anomalies and mantle like whole rock nd sr isotopic compositions e nd t 2 5 to 4 5 87 sr 86 sr i 0 7038 to 0 7048 and zircon e hf t values 5 93 to 12 9 the mmes contain abundant magmatic amphiboles and needle like apatites have low sio 2 51 7 to 54 3 wt and high mgo 2 86 to 3 75 wt and ree contents 162 298 ppm and are characterized by moderately negative eu anomalies eu eu 0 40 0 60 and slightly depleted to enriched lree la nd n 0 74 1 41 and flat hree gd yb n 1 16 1 39 patterns the mmes have whole rock nd sr isotopic compositions e nd t 2 6 to 2 7 87 sr 86 sr i 0 7034 0 7050 similar to those of the host granodiorites their similarities in crystallization age mineral assemblage and isotopic composition document that the mmes may represent an early crystallized phase which was broken into pieces and brought to the shallow level during the host magma ascent and emplacement their precursor magmas were probably derived from an oceanic lithospheric mantle which was characterized by pronounced nd ta depletions mineral compositions of mmes suggest that amphibole was a major early fractional mineral which effectively differentiated the mantle derived basaltic liquids to silica rich melts zircon u pb dating yielded an age of 313 5 ma for the host granodiorites and 313 13 ma for their mmes the geochemical data of this study records an important episode of magmatism in an environment transitional from a subduction related regime to a post tectonic extension results of this study suggest that the accretionary orogenic process did not completely terminate until the late carboniferous to permian in this region

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

teleconnected influence of north atlantic sea surface temperature on the el nino onset influence of north atlantic sea surface temperature sst anomalies on tropical pacific sst anomalies is examined both summer and winter north atlantic sst anomalies are negatively related to central eastern tropical pacific sst anomalies in the subsequent months varying from 5 to 13 months in particular when the north atlantic is colder than normal in the summer an el nino event is likely to be initiated in the subsequent spring in the tropical pacific associated with summer cold north atlantic sst anomalies is an anomalous cyclonic circulation at low level over the north atlantic from subsequent october to april corresponded to this local response an sst induced heating over the north atlantic produces a teleconnected pattern similar to the east atlantic west russia teleconnection the pattern features two anticyclonic circulations near england and lake baikal and two cyclonic circulations over the north atlantic and near the caspian sea the anticyclonic circulation near lake baikal enhances the continent northerlies and strengthens the east asian winter monsoon these are also associated with an off equatorial cyclonic circulation in the western pacific during the subsequent winter and spring which produces equatorial westerly wind anomalies in the western pacific the equatorial westerly wind anomalies in the winter and spring can help initiate a pacific el nino event following a cold north atlantic in the summer