along arc lateral variation of rb sr and k ar ages of cretaceous granitic rocks in southwest japan cretaceous granitic rocks were emplaced over a distance of 700 km along arc in southwest japan rb sr and k ar ages of a major group of these granitic rocks with ilmenite series ore mineralogy were examined rb sr whole rock ages of 92 8 4 0 ma and rb sr and k ar biotite ages of 80 88 ma were obtained on one group of these granitic rocks from kamo sera area of central hiroshima prefecture the k ar ages of various minerals combined with the rb sr whole rock age give a smooth cooling curve which suggests a 5 to 10 ma time lag between intrusion and cooling at 300 c for the cretaceous granitic rocks the rb sr whole rock and rb sr k ar biotite ages of these granitic rocks become younger eastward along the southwest japan arc and the time lag between the two systems remains constant at 5 to 10 ma over the entire area the along arc age variation does not support the genetical relationship of the cretaceous granitoids with steady state subduction the cretaceous granitic province at the eastern margin of eurasian continent was at least partly formed by an episodic event such as ridge subduction

role of nonlinear ocean dynamic response to wind on the asymmetrical transition of el nino and la nina to understand why el nino is frequently followed by la nina while the opposite occurs rarely we analyze the inherent asymmetry in a delayed negative feedback loop in the framework of delayed oscillator theory using observational data the asymmetrical response of the ocean wave to wind is much larger than that of the wind intensity to sst and that of the subsurface temperature to thermocline strong oceanic response during el nino compared to la nina is presumably due to the relatively shallow mean thermocline over the western pacific which efficiently traps the atmospheric momentum in the shallow upper ocean and the asymmetrical wind pattern response to sst a modified delayed oscillator model experiment verifies that the asymmetrical ocean wave response to wind is more important in the asymmetrical transition of el nino and la nina than asymmetrical wind intensity response to sst and asymmetrical subsurface temperature response to thermocline

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

the normality of el nino the amplitude of the el nino southern oscillation enso would be normally distributed if the coupled pacific ocean atmosphere were a linear system forced by gaussian weather noise moment estimates of skewness and kurtosis demonstrate that this is not the case for monthly mean anomalies in pacific sea surface temperatures during 1950 97 the noted predominance of el nino events compared to la nina events is related to the high skewness in the eastern pacific skewness and kurtosis both exhibit an intriguing geographical variation from positive in the eastern to negative in the western pacific we have also examined nino 3 indices generated by three climate models having widely different complexity these exhibit a wide range of skewness and kurtosis values rather different from those found for the observations skewness and kurtosis can be used to diagnose non linear processes and provide powerful tools for validating models and for testing observed sea surface temperatures for the presence of possible climate change

post magmatic cooling of the elberton granite bearing on the late paleozoic tectonothermal history of the georgia inner piedmont the elberton granite is an undeformed pluton which intrudes polydeformed gneisses along the eastern margin of the georgia inner piedmont magmatic biotite and muscovite display internally concordant 40 ar 39 ar release spectra which record plateau dates of 235 241 m y biotite from adjacent gneisses and from recrystallized xenoliths yield similar plateau ages hornblende from country rock amphibolite and from recrystallized xenoliths record well defined 40 ar 39 ar plateau ages of 267 276 m y the 40 ar 39 ar ages are markedly younger than the 320 20 m y crystallization age of the pluton u pb zircon ross and bickford 1980 and are interpreted to date times of post magmatic cooling through temperatures required for argon retention in the various mineral species examined because similar ages are recorded by equivalent minerals from the country rock terrane post magmatic cooling must have closely followed post metamorphic cooling of the inner piedmont 40 ar 39 ar date

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

crust enriched mantle derived tonalites in the early proterozoic penokean orogen of wisconsin the early proterozoic 1 82 to 1 89 ga penokean orogenic province represents the initial phase of a major period of crustal growth of the north american proterozoic craton in central wisconsin the orogeny is dominated by the intrusion of variably deformed and metamorphosed tonalite trondhjemite suites in part hosted by archean gneisses and migmatites the magmatism is calc alkaline and similar in composition to modern high k orogenic andesites moderate abundances of sr 600 750 ppm and ree in the most primitive tonalites are consistent with derivation from an eclogitic altered tholeiite rather than a crustal archean amphibolitic tholeiite or enriched mantle source existing nd sr isotopic data for other tonalites of the wisconsin penokean orogen also indicate a mantle origin but with some admixture of archean crustal component this study shows that an archean component most likely was incorporated during emplacement the tonalite to trondhjemite differentiation of these magmatic suites is not

is enso a cycle or a series of events 1 after early ideas that saw el ninos as isolated events the advent of coupled models brought the conception of enso as a cycle in which each phase led to the next in a self sustained oscillation twenty two years of observations that represent the el nino and la nina peaks east pacific sst and the memory of the system zonal mean warm water volume suggest a distinct break in the cycle in which the coupled system is able to remain in a weak la nina state for up to two years so that memory of previous influences would be lost similarly while the amplitude of anomalies persists from the onset of a warm event through its termination there is no such persistence across the la nina break these observations suggest that el ninos are in fact event like disturbances to a stable basic state requiring an initiating impulse not contained in the dynamics of the cycle itself

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

equatorial pacific easterly wind surges and the onset of la nina events abstractthe processes responsible for the onset of la nina events have not received the same attention as those responsible for the onset of el nino events for which westerly wind events wwes in the tropical pacific have been identified as important contributors results here show that synoptic scale surface easterly wind surges ewss play an important role in the onset of la nina events akin to the role of wwes in the onset of el nino events it is found that ewss are a substantial component of zonal wind stress variance along the equatorial pacific using reanalysis wind stress fields validated against buoy measurements 340 ews events are identified between 1986 and 2012 their distributions in space time and el nino southern oscillation enso state are described about 150 ewss occur during enso neutral conditions during the months associated with la nina initiation and growth april december composites of changes in sea surface temperature anomaly ssta following these 150 events show s

paleomagnetic history of the mealy dykes of labrador canada paleomagnetic analysis of the mealy diabase dykes of labrador reveals magnetizations that predate the grenville event at about 1000 ma these dykes intrude the mealy mountains anorthositic complex in the grenville structural province they are well south of the grenville front tectonic zone but were apparently never subjected to temperatures as high as 500 c during their post consolidation history four distinct magnetic components were uncovered by thermal and alternating field treatments and a fifth remained unresolved the major magnetic mineral present titanomagnetite is thought to record two magnetic directions acquired during cooling from magmatic temperatures these are b d 305 i 76 n 18 sites 12 95 11 and a d 095 i 52 n 20 sites 46 95 5 component b has much within site dispersion the other two components c d 274 i 47 n 10 sites 15 95 13 and d d 292 i 74 5 95 31 probably reside in magnetite and pyrrhotit

the geochemistry of the la galissonniere pluton a middle proterozoic late orogenic intrusion from the eastern grenville province quebec the la galissonniere pluton is a late orogenic pluton located in the eastern grenville province of quebec the pluton contains biotite hornblende zircon titanite allanite and apatite along with secondary sericite and epidote the pluton features elevated values of nb y and f the normalized rare earth element patterns have light rare earth element concentrations of 400 500 chondrite moderate slopes 10 20 and noticeable eu anomalies trace element discriminant diagrams suggest that the pluton formed in a late orogenic environment and indicate a possible period of late precambrian crustal attenuation in the eastern grenville province

asymmetry in the duration of el nino and la nina abstract el nino and la nina are not a simple mirror image but exhibit significant differences in their spatial structure and seasonal evolution in particular sea surface temperature sst anomalies over the equatorial pacific cold tongue are larger in magnitude during el nino compared to la nina resulting in positive skewness of interannual sst variations the associated atmospheric deep convection anomalies are displaced eastward during el nino compared to la nina because of the nonlinear atmospheric response to sst in addition to these well known features an analysis of observational data for the past century shows that there is a robust asymmetry in the duration of el nino and la nina most el ninos and la ninas develop in late boreal spring summer when the climatological cold tongue is intensifying and they peak near the end of the calendar year after the mature phase el ninos tend to decay rapidly by next summer but many la ninas persist through the following year and often reintensify in

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

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

paleomagnetic evidence for the continuity and independent movement of a distinct major crustal block in the southern appalachians the magnetization of 22 granitic and gneissic southern appalachian rock units with estimated cooling ages of 415 250 m y has been determined included are 842 samples from 114 sites within 19 granites 100 sites and 3 gneisses 14 sites located in north carolina south carolina and georgia data for units which cooled to temperatures 20 000 km sup 2 in size a mean paleopole for this group with corrections for maximum tilt estimates exhibits good precision but has a paleosite latitude of approx 10 sup 0 n without tilt correction the paleopole for group b still exhibits an anomalous paleositemore latitude of approx 4 sup 0 n these data indicate that the group b block elberton sparta crustal block lying to the se has an apparent paleosite latitude corresponding to magnetization at a location to the north of the zone containing group a units less

ages of regional metamorphism and ductile deformation in the central and southern appalachians abstract a summary of available geochronology of deformational fabrics formed at greenschist and higher grades in the central and southern appalachians is presented as a map showing the ages of regional metamorphism and ductile deformation the ca 480 435 ma taconic event affected most of the piedmont and blue ridge provinces the ca 380 340 ma acadian event was milder and was centered in the west central piedmont and eastern blue ridge the 330 230 ma alleghanian event exhibits an abrupt ductile deformation front in the eastern piedmont and extends an unknown distance eastward below the atlantic coastal plain

wide angle seismic imaging of the elberton granite georgia a pilot study using instantaneous blasts at dimension stone quarries abstractwide angle recordings of small multiple hole blasts at dimension stone quarries in the elberton granite show coherent reflections at offsets between 7 and 15 km in contrast with much larger blasts at crushed stone quarries this type of blast is fired without delays between holes the data were recorded with an array of twenty portable seismographs using three component 4 5 hz geophones migration of source gathers for two of the blasts shows a number of subhorizontal interfaces at depths between 2 and 4 km that may represent a layered complex near the base of the granite other reflectors include southeast dipping interfaces at depths between 6 and 9 3 km and a more gently southeast dipping complex at 9 5 11 km that may represent the master decollement the results of the pilot study show that this type of quarry blast can be useful for imaging structure within the upper crust although preliminary the wide angle results support the interpretation that the elberton granite is a tabular body l

s type granites and their probable absence in southwestern north america criteria that have been and still are used to characterize s type granites of the lachlan fold belt lfb of southeastern australia are reviewed and comparisons are made with various peraluminous granites of southwestern north america some of which have been classified as s types on the basis of insufficient data virtually all of the vast volume of s type granites in the lfb are near surface batholithic granites that are commonly associated with s type volcanics and are not associated with regional metamorphic rocks and migmatites they are strongly peraluminous as shown by the presence of cordierite granites with primary muscovite are rare all are low in na ca and sr as a result of chemical weathering during formation of the sedimentary sources peraluminous granites of various ages in southwestern north america are distinctly different they rarely contain cordierite a mineral characteristic of lfb s types but some are highly evolved such that fe mn rich garnet has crystallized they are dominantly two mica granites indicating crystallization at higher water fugacities and greater depths than most peraluminous granites of the lfb cordierite bearing volcanics s types have not been reported sodium is generally high in the peraluminous granites of southwestern north america some of these rocks have trondhjemitic affinities the parent magmas seem more likely to have been produced by partial melting of altered basaltic rocks locally some peraluminous rocks marginal to metaluminous types may owe their compositions to high level contamination of i types these are not s type rocks no compelling evidence has been presented that any of the peraluminous granites of southwestern north america are s types

the scale of sr isotopic diffusion during post metamorphic cooling of gneisses in the inner piedmont of georgia southern appalachians abstract rb sr whole rock isotopic analyses of two suites of contiguous gneiss samples each ca 10 cm in width collected in quarries within the georgia inner piedmont of the southern appalachians indicate that sr isotopic diffusion continued on a scale of 10 25 cm for at least 30 ma after culmination of high grade regional metamorphism variation of rb sr ratios between 14 contiguous slabs of one suite is sinusoidal about an overall mean of 1 5 permitting calculation of a 315 17 ma isochron on the basis of previous estimates of the scale of sr diffusion in feldspar under geological conditions an approximate closure temperature of 600 c may be calculated together with rb sr and 40 ar 39 ar mineral ages from this quarry the 315 17 ma isochron age is interpreted to date cooling through ca 600 c following culmination of high grade devonian regional metamorphism the average rb sr isotopic composition of a contiguous suite from another inner piedmont quarry confirms a paleozoic age for regional metamorphism

a proposed mechanism for the asymmetric duration of el nino and la nina el nino and la nina exhibit significant asymmetry not only in their spatial structure but also in their duration most el ninos terminate rapidly after maturing near the end of the calendar year whereas many la ninas persist into the following year and often reintensify in boreal winter through atmospheric general circulation model experiments it is shown that the nonlinear response of atmospheric deep convection to the polarity of equatorial pacific sea surface temperature anomalies causes an asymmetric evolution of surface wind anomalies over the far western pacific around the mature phase of el nino and la nina because of the eastward displacement of precipitation anomalies in the equatorial pacific during el nino compared to la nina surface winds in the western pacific are more affected by sst forcing outside the equatorial pacific which acts to terminate the pacific event

paleomagnetism of some mafic intrusions in the south carolina piedmont i magnetic systems with single characteristic directions abstract four mafic and two dioritic igneous bodies intruding along the flanks of the charlotte belt within the king s mountain belt and near the slate kiokee charlotte belt boundaries in the south carolina piedmont were studied paleomagnetically the results suggest that these mafic rocks with a single characteristic magnetization are broadly contemporaneous a mean paleomagnetic pole position of 38 9 n 120 8 e has been calculated for the six bodies this pole position falls near the 300 ma old point of irving s apparent polar wander path apwp for north america the 95 circle of confidence 10 2 includes points on the apwp between 250 360 ma anomalously old k ar apparent ages greater than one billion years are suggestive of excess 40 ar contamination for the mafic buffalo pluton whereas apparent ages in the range of 360 395 ma old are interpreted as a maximum age for the other bodies due to the possibility of small amounts of excess 40 ar being present a 10 westerly tilt correction suggested by dooley and smith for early mesozoic diabase brings the mafic pole position of this study to more nearly coincide with the 350 ma virtual geomagnetic position of irving s curve but the test is inconclusive awaiting better definition of radiometric ages the simplest interpretation of the data is that the mafic pole position reflects the direction of the geomagnetic field in late devonian carboniferous times the similarity of this pole position with the points on the apwp for north america provides little evidence for displaced terrains and with the precision of this pole position horizontal displacements on the order of that suggested by the consortium for continental reflection profile cocorp results or by subsequent studies are not detectable this and other pole positions from granitic rocks in the southern appalachian orogen suggest that if displaced terrains exist the evidence must be found in older rocks or in other geologic belts

asymmetry in zonal phase propagation of enso sea surface temperature anomalies 1 it is often emphasized in the literature that the phase propagation of el nino sea surface temperature sst anomalies along the equator changed from westward to eastward after a mid to late 1970s climate regime shift in the pacific theories have been developed to explain this change of phase propagation in terms of changes in background state on which el nino events develop those theories also suggest that the direction of la nina anomaly phase propagation should have changed from westward to eastward as well however the direction of la nina sst anomaly phase propagation did not change after the mid to late 1970s instead la nina ssts continued to exhibit westward phase propagation along the equator a feature overlooked in both observational analyses and theories this paper highlights the asymmetry in zonal phase propagation between el nino and la nina sea surface temperature anomalies since 1980 and discusses the implications of that asymmetry for understanding el nino southern oscillation enso dynamics

el nino and la nina sea surface temperature anomalies asymmetry characteristics associated with their wind stress anomalies 1 the asymmetric nature of el nino and la nina sea surface temperature sst anomalies is investigated by the use of national centers for environmental prediction reanalysis data and various ocean and atmosphere models it is demonstrated that the relatively weak sst anomalies during la nina compared with those of el nino are related to the westward shift of wind stress anomalies by 10 15 the asymmetric characteristics of atmospheric responses are confirmed by the general circulation model experiments with the two different sst anomalies which have equal amplitude but are of opposite sign from each other the experiments with an intermediate ocean model and a hybrid coupled model clearly show that the sst anomalies over the equatorial pacific become weaker as the zonal wind stress shifts to the west not only the amplitude but also the oscillation timescale of the sst anomaly is shown to be sensitive to the location of wind stress anomalies the duration of la nina which is rather shorter than that of el nino is also related to the longitudinal displacement of the wind stress anomaly

the role of reversed equatorial zonal transport in terminating an enso event abstractthis study shows the sudden basinwide reversal of anomalous equatorial zonal transport above the thermocline at the peaking phase of enso triggers rapid termination of enso events the anomalous equatorial zonal transport is controlled by the concavity of anomalous thermocline meridional structure across the equator during the developing phase of enso opposite zonal transport anomalies form in the western central and central eastern equatorial pacific respectively both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western central equatorial ocean at this stage the anomalous zonal transport in the east enhances enso growth through zonal sst advection in the mature phase of enso off equatorial thermocline depth anomalies become more dominant in the eastern pacific because of the reflection of equatorial signals at the eastern boundary as a result the meridional concavity of the thermocline anomalies is reversed in the east this change reve

combination mode dynamics of the anomalous northwest pacific anticyclone abstractnonlinear interactions between enso and the western pacific warm pool annual cycle generate an atmospheric combination mode c mode of wind variability the authors demonstrate that c mode dynamics are responsible for the development of an anomalous low level northwest pacific anticyclone nwp ac during el nino events the nwp ac is embedded in a large scale meridionally antisymmetric indo pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in asia in contrast to previous studies the authors find the role of air sea coupling in the indian ocean and northwestern pacific only of secondary importance for the nwp ac genesis moreover the nwp ac is clearly marked in the frequency domain with near annual combination tones which have been overlooked in previous indo pacific climate studies furthermore the authors hypothesize a positive feedback loop involving the anomalous low level nwp ac through el nino and c mode interactions the development o

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

changes in tropical pacific thermocline depth and their relationship to enso after 1999 abstractthe characteristics of el nino southern oscillation enso variability have experienced notable changes since the late 1990s including a breakdown of the zonal mean upper ocean heat content as a precursor for enso these changes also initiated a debate on the role of thermocline variations on the development of enso events since the beginning of the twenty first century in this study the connection between thermocline variations and el nino and la nina events is examined separately for the 1980 98 and 1999 2012 periods the analysis highlights the important role of thermocline variations in modulating enso evolutions in both periods it is found that thermocline variation averaged in the central tropical pacific including both equatorial and off equatorial regions is a good precursor for enso evolutions before and after 1999 while the traditional basinwide mean of equatorial thermocline variation is a good precursor only before 1999 the new precursor including both high frequency variabili

an example of trondhjemite petrogenesis the blakes ferry pluton alabama u s a abstract the blakes ferry pluton is a calc alkaline pluton that is exposed in southwestern randolph county alabama u s a the petrogenesis of the blakes ferry pluton has been a controversy for almost 15 years a petrogenetically coherent model is presented however as a result of new mineral analyses and the examination of previous analytical data crystal fractionation of plagioclase has been substantiated based on mass balance calculations assimilation crystal fractionation modelling and mixing calculations suggest that the biotite muscovite sphene rich schlieren observed within the blakes ferry pluton are remnants of partially assimilated metasedimentary rock furthermore the biotite chemistry of the blakes ferry pluton is quite similar to that of the biotites in the wedowee schists which are the host rock to the blakes ferry intrusion the above indicates the assimilation mixing of the wedowee metasediments occurred toward the end of plagioclase fractionation the blakes ferry pluton has both l and s type characteristics interpreted as inherited from the source melting of an igneous rock with subsequent assimilation of the metasediments surrounding the pluton the elkahatchee quartz diorite a large older tonalitic intrusive near the blakes ferry pluton has been ruled out as a potential source rock contrary to previous interpretations crystal fractionation of a more mafic magma e g gabbro to generate the blakes ferry melt also does not seem plausible because the associated sequence of differentiated products are not observed in the region based on ree modelling and experimental work the only plausible source is the partial melting of a morb with a hornblende quartz eclogite residual the most likely source for the partial melting of a morb is in a subduction related environment several researchers have proposed an arc setting for associated rocks within the same structural and metamorphic block that the blakes ferry poluton is situated this suggests that the necessary setting for the partial melting of morb was present in the region the partial melting of approximately 28 morb coupled with the generation of 72 hornblende quartz eclogite residual in a subduction zone is envisioned the density differences between the trondhjemitic melt and the surrounding mantle generated the ascent of the magma plagioclase fractionation via filter pressing probably occurred during ascent the magma stalled in the wedowee metasediments because the density contrasts no longer existed between melt and surrounding rocks assimilation and further fractional crystallization took place as the magma cooled to become the trondhjemitic schlieren rich body observed in the field today

season dependent predictability and error growth dynamics for la nina predictions the spring predictability barrier spb is a well known characteristic of enso prediction which has been widely studied for el nino events however due to the nonlinearity of the coupled ocean atmosphere system and the asymmetries between el nino and la nina it is worthy to investigate the spb for la nina events and reveal their differences with el nino this study investigates the season dependent predictability of sea surface temperature sst for la nina events by exploring initial error growth in a perfect model scenario within the community earth system model the results show that for the prediction through the spring season the prediction errors caused by initial errors have a season dependent evolution and induce an spb for la nina events two types of initial errors that often yield the spb phenomenon are identified the first are type 1 initial errors showing positive sst errors in the central eastern equatorial pacific accompanied by a large positive error in the upper layers of the eastern equatorial pacific the second are type 2 errors presenting an sst pattern with positive errors in the southeastern equatorial pacific and a west east dipole pattern in the subsurface ocean the type 1 errors exhibit an evolving mode similar to the growth phase of an el nino like event while the type 2 initially experience a la nina like decay and then a transition to the growth phase of an el nino like event both types of initial errors cause positive prediction errors for nino3 sst and under predict the corresponding la nina events the resultant prediction errors of type 1 errors are owing to the growth of the initial errors in the upper layers of the eastern equatorial pacific for the type 2 errors the prediction errors originate from the initial errors in the subsurface layers of the western equatorial pacific these two regions may represent the sensitive areas of targeted observation for la nina prediction in addition the type 2 errors in the equatorial regions are enlarged by the recharge process from 10 n in the central pacific during the eastward propagation therefore the off equatorial regions around 10 n in the central pacific may represent another sensitive area of la nina prediction additional observations may be prioritized in these identified sensitive areas to better predict la nina events

meridional movement of wind anomalies during enso events and their role in event termination 1 observational analysis has shown that when el nino southern oscillation enso events typically reach their peak amplitude in boreal winter the associated zonal wind anomalies abruptly shift southward so that the maximum anomalous zonal wind is located around 5 7 s here an analysis utilizing multiple wind products identifies a clear enso phase nonlinearity in the extent of this meridional wind movement and its dynamically linked changes in equatorial heat content it is shown that the meridional wind movement and its discharging effect increase with increasing el nino amplitude while both remain relatively small regardless of la nina amplitude this result implies that asymmetries in the extent of the meridional wind shift may contribute to the observed asymmetry in the duration of el nino and la nina events we also evaluate the result sensitivities to wind product selection and discuss eastern pacific ep and central pacific cp el nino event differences

cold tongue and warm pool enso events in cmip5 mean state and future projections abstractthe representation of the el nino southern oscillation enso under historical forcing and future projections is analyzed in 34 models from the coupled model intercomparison project phase 5 cmip5 most models realistically simulate the observed intensity and location of maximum sea surface temperature sst anomalies during enso events however there exist systematic biases in the westward extent of enso related sst anomalies driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western pacific almost all cmip5 models capture the observed asymmetry in magnitude between the warm and cold events i e el ninos are stronger than la ninas and between the two types of el ninos that is cold tongue ct el ninos are stronger than warm pool wp el ninos however most models fail to reproduce the asymmetry between the two types of la ninas with ct stronger than wp events which is opposite to observations most models capture the observed peak in enso

geologic setting of the hillabee metavolcanic complex and associated strata bound sulfide deposits in the appalachian piedmont of alabama the frontal crystalline thrust sheet of the southern appalachians in alabama is a sequence of lower greenschist facies rocks known as the talladega slate belt this sequence is composed dominantly of metapelites and metasandstones but it contains a distinctive metavolcanic complex the hillabee greenstone at the stratigraphic top sulfide deposits occur throughout the 170 km outcrop extent of the hillabee the metavolcanics are bounded above by thrust faults which have emplaced nappes containing medium to high grade rocks of the ashland and wedowee sequences the hillabee greenstone is as much as 2 6 km thick in some areas but is only a few 100 m thick in most places because of the stratigraphic position of the thrust faults low k tholeiitic rocks constitute the bulk of the metavolcanic rocks calc alkaline quartz dacites are common the hillabee greenstone appears to be the distal continentward portion of a volcanic arc system which developed during the middle paleozoic in the southernmost appalachians the basal dominantly pyroclastic part of the volcanic sequence is interlayered with the upper part of the talladega group which locally contains a lower to middle devonian fossil assemblage in the north central part of the belt near pyriton strata bound massive sulfide deposits are common very near the base of the volcanic sequence the deposits appear to be distal strata bound zn cu pyrite type other strata bound deposits occur in mafic rocks immediately above siliceous metavolcanic rocks in the broad central part of the belt which appears to be dominated by basalt flows disseminated sulfides are common in this central region as well

subduction products according to experimental prediction knowledge of the thermal structure and processes in subduction zones is so uncertain that our more extensive knowledge of source materials and phase relationships remains insufficient for prediction of magmatic products the phase relationships do provide important constraints for testing geophysical and petrogenetic models especially when considered along with geochemical constraints physical questions such as the behavior of partially molten rocks are intimately related to the compositions of magmas from source to eruption site tentative predictions and conclusions include 1 andesite is not a primary magma from oceanic crust 2 it is unlikely that liquids from subducted oceanic crust yield andesites by fractionation except by melting of amphibolite in an especially warm subducted crust 3 it is more likely that hydrous siliceous magmas from the crust leak into the overlying mantle 4 andesite magmas can be generated in peridotite only under exceptional circumstances 5 h2o undersaturated basic magmas from peridotite modified by aqueous fluids or hydrous magma may yield andesite by fractionation 6 phlogopite peridotite could escape melting and yield alkalic magmas at deeper levels 7 andesite magmas could be produced in continental crust only by extreme heating through underplating of basalts or by mixing of basalt and rhyolite derived from crust most of these conclusions need revision if convection in the asthenosphere wedge raises the temperature of the subducted slab to 1250 c at 100 km as proposed by marsh 1979a this demonstrates the dependence of experimental predictions on geophysical models

rbsr dating of acidic rocks from the middle part of the inner zone of southwest japan tectonic implications for the migration of the cretaceous to paleogene igneous activity abstract rb sr age determinations by mineral and whole rock isochron methods have been performed on cretaceous to paleogene granitic and rhyolitic rocks from the middle part of the inner zone of southwest japan in order to examine some chronological problems and tectonic models for the migration of igneous activity our chronological results include 1 isotopic homogenization of granitic and rhyolitic rocks in the miyazu izushi area was disturbed by mixing of acidic and basic magmas 2 the rokko granite was emplaced at 77 8 ma and reheated at 72 ma 3 mineral isochron ages obtained for the acidic volcanic rocks range from 62 6 to 85 8 ma and are considered to date the time of eruption igneous activity migrated eastward from 95 ma to 70 ma which may be related to a similar eastward migration of the development of sedimentary basins in fore arc regions the observed eastward migration has been discussed with relevance to a ridge subduction model in which the heated position by subducted ridge moved from west to east although the cause for the migration of the igneous activity is poorly understood several difficulties with the simple ridge subduction model are pointed out

understanding key roles of two enso modes in spatiotemporal diversity of enso abstractel nino southern oscillation enso events exhibit a diversity of amplitudes spatial patterns and life cycles while the 3 7 yr low frequency lf and 2 3 yr quasi biennial qb bands co

interannual and interdecadal variability of ocean temperature along the equatorial pacific in conjunction with enso in this paper the leading modes of ocean temperature anomalies ota along the equatorial pacific ocean are analyzed and their connection with el nino southern oscillation enso and interdecadal variation is investigated the first two leading modes of ota are connected with the different phases of the canonical enso and display asymmetric features of enso evolution the third leading mode depicts a tripole pattern with opposite variation of ota above the thermocline in the central pacific to that along the thermocline in the eastern and western pacific this mode is found to be associated with so called enso modoki insignificant correlations of this mode with the first two leading modes suggest that enso modoki may be a mode that is independent to the canonical enso and also has longer time scales compared with the canonical enso the fourth mode reflects a warming cooling tendency above below the thermocline since 2000 both the first and second modes have a large contribution to the interdecadal change in thermocline during 1979 2012 also the analysis also documents that both enso and ota shifted into higher frequency since 2000 compared with that during 1979 1999 interestingly the enso modoki related ota mode does not have any trend or significant interdecadal shift during 1979 2012 in addition it is shown that first four eof modes seem robust before and after 1999 2000 suggesting that the interdecadal shift of the climate system in the tropical pacific is mainly a frequency shift and the changes in spatial pattern are relatively small although the mean states over two periods experienced some significant changes

enso and east asian winter monsoon relationship modulation associated with the anomalous northwest pacific anticyclone using observational datasets and numerical model experiments the mechanism on the slowly varying change in the relationship between the el nino southern oscillation enso and the east asian winter monsoon eawm is investigated the decadal window 11 15 and 21 year moving correlations show a significant change in the boreal wintertime enso eawm relationship between two sub periods of 1976 1992 and 1997 2013 such recent change in enso eawm relationship is mainly attributed to the changes in the intensity and zonal location of the anomalous lower tropospheric northwest pacific anticyclone nwp ac nwp ac commonly develops near the region of the philippine sea during the enso s peak phase and plays an important role of bridging the tropical convection and mid latitude teleconnection on one hand the intensity of the nwp ac is influenced by the interdecadal variation in a linkage between enso and the indian ocean sea surface temperature sst variability referring that a strong connection between the pacific and indian oceans results in the strengthening of nwp ac response to enso on the other hand the zonal displacement of the nwp ac is associated with the pacific decadal oscillation pdo and the atlantic multidecadal oscillation amo that is the tropical pacific mean state i e zonal sst gradient between climatologically warm western pacific and cold eastern pacific strengthened by either the negative pdo phase or the positive amo phase drives the anomalous enso induced convection to be shifted to the west with this westward shift the zonal center of the nwp ac also migrates westward over the philippine islands and exerts stronger connection between enso and eawm in contrast the relaxed zonal sst contrast associated with either the positive pdo phase or the negative amo phase tends to exhibit weaker enso eawm relationship via both of eastward shifted zonal centers of the anomalous enso induced convection and the nwp ac finally a series of the numerical experiments conducted by an atmospheric general circulation model supports the observational findings

potential impact of the tropical indian ocean indonesian seas on el nino characteristics diagnostics performed with twentieth century 1861 2000 ensemble integrations of the geophysical fluid dynamics laboratory climate model version 2 1 cm2 1 suggest that during the developing phase el nino events that co occur with the indian ocean dipole zonal mode iodzm class 1 are stronger than those without class 2 also during class 1 events coherent sea surface temperature sst anomalies develop in the indonesian seas that closely follow the life cycle of iodzm this study investigates the effect of these regional sst anomalies equatorial indian ocean and indonesian seas on the amplitude of the developing el nino an examination of class 1 minus class 2 composites suggests two conditions that could lead to a strong el nino in class 1 events i during january ocean atmosphere conditions internal to the equatorial pacific are favorable for the development of a stronger el nino and ii during may june coinciding with the development of regional sst anomalies an abrupt increase in westerly wind anomalies is noticeable over the equatorial western pacific with a subsequent increase in thermocline and sst anomalies over the eastern equatorial pacific this paper posits the hypothesis that under favorable conditions in the equatorial pacific regional sst anomalies may enable the development of a stronger el nino owing to a wealth of feedbacks in cm2 1 solutions from a linear atmosphere model forced with may june anomalous precipitation and anomalous sst from selected areas over the equatorial indo pacific are examined consistent with our earlier study the net kelvin wave response to contrasting tropical indian ocean heating anomalies cancels over the equatorial western pacific in contrast indonesian seas sst anomalies account for about 60 80 of the westerly wind anomalies over the equatorial western pacific and also induce anomalous precipitation over the equatorial central pacific it is argued that the feedback between the precipitation and circulation anomalies results in an abrupt increase in zonal wind anomalies over the equatorial western pacific encouraged by these results the authors further examined the processes that cause cold sst anomalies over the indonesian seas using an ocean model sensitivity experiments suggest that local wind anomalies through stronger surface heat loss and evaporation and subsurface upwelling are the primary causes the present results imply that in coupled models a proper representation of regional air sea interactions over the equatorial indo pacific warm pool may be important to understand and predict the amplitude of el nino

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

contact aureoles as constraints on regional p t trajectories an example from the northern alabama piedmont usa contact aureoles of plutons emplaced into regionally metamorphosed terranes can provide indicators of physical conditions along a portion of regional metamorphic p t trajectories thereby allowing reconstruction of more complete p t loops than would be otherwise possible in the northern alabama piedmont of the southern appalachians wedowee group metapelites preserve evidence for two regional metamorphic phases overprinted by contact metamorphism adjacent to the blakes ferry trondhjemite textural evidence indicates that an early bt st grt assemblage was replaced by bt chl grt during the latter stages of regional metamorphism changes in akfm topology complex fe mg ca garnet zoning and the latestage appearance of epidote indicate that a sequence of continuous reactions bt st grt ms followed by chl ms ca grt ca pl bt fe mg grt ep occurred in response to increasing pressure and resulted in the observed changes in mineral assemblage pl ms bt grt thermobarometry indicates conditions of 580 65 c 8 5 0 8 kbar for equilibration of grt bt chl pluton emplacement subsequent to penetrative deformation caused textural annealing and mineral re equilibration by the continuous reaction bt fe mg grt ep chl ms ca grt ca pl within 50 m of the pluton conditions of 510 65 c 5 7 kbar are inferred a reconstructed p t trajectory for this area is characterized by 1 early moderate t moderate p metamorphism 2 an increase in p to approximately 8 5 kbar and 3 decompression and slight cooling prior to pluton emplacement the compressional phase of this path is interpreted to result from underthrusting of the wedowee metasediments to mid crustal levels during palaeozoic crustal thickening late stage decompression prior to intrusion records uplift of these rocks in response to movement on structurally lower thrusts

why were some la ninas followed by another la nina this paper investigates why some la nina events are followed by another la nina and some others are not we propose two preconditions that result in continuation of a la nina the first one is that la nina must be a strong event a major la nina this ensures that the reflected rossby wave signal at the eastern boundary of the pacific has a strong westward propagating cold ocean temperature anomaly over the off equatorial region the off equator cold anomaly may not be conducive to the equatorial recharge process and as a result may favor the persistence of cold ocean subsurface temperature anomaly and prevent the transition from la nina to el nino the second precondition is whether there are eastward propagating downwelling kelvin waves during the decay phase of a major la nina eastward propagating downwelling kelvin waves could lead to demise for a tendency for a follow up la nina the equatorial kelvin wave activities are associated with fluctuations of surface wind in the equatorial far western pacific the analysis suggests that both the surface wind in the equatorial far western pacific and the recharge discharge of the equatorial pacific are indicators for occurrence or no occurrence of a follow up la nina event

the role of the southward wind shift in both the seasonal synchronization and duration of enso events near the end of the calendar year when el nino events typically reach their peak amplitude there is a southward shift of the zonal wind anomalies which were centred around the equator prior to the event peak previous studies have shown that enso s anomalous wind stresses including this southward shift can be reconstructed with the two leading eofs of wind stresses over the tropical pacific here a hybrid coupled model is developed featuring a statistical atmosphere that utilises these first two eofs along with a linear shallow water model ocean and a stochastic westerly wind burst model this hybrid coupled model is then used to assess the role of this meridional wind movement on both the seasonal synchronization as well as the duration of the events it is found that the addition of the southward wind shift in the model leads to a christmas peak in variance similar to the observed timing although with weaker amplitude we also find that the added meridional wind movement enhances the termination of el nino events making the events shorter while this movement does not appear to play an important role on the duration of la nina events thus our results strongly suggest that the meridional movement of enso zonal wind anomalies is at least partly responsible for seasonal synchronization of enso events and the duration asymmetry between the warm el nino and cool la nina phases

the mealy dykes labrador petrology age and tectonic significance the mealy dykes constitute a major olivine diabase swarm in the mealy mountains grenville province labrador the dykes intrude anorthosites and monzonites of the mealy mountains complex and outcrop over an area of at least 4000 km2 the swarm strikes east northeast and may constitute the largest group of unmetamorphosed diabase dykes in the grenville province the mealy dykes are moderately iron rich olivine tholeiites typically nonporphyritic thick dykes have coarse grained interiors that show some fractionation but variations in bulk chemical composition are relatively modest olivine fo47 fo27 plagioclase cores an63 an47 rims an47 an30 and low ca augite are the principal silicate minerals coexisting magnetite and ilmenite suggest that solidus temperatures were about 980 c and that subsolidus oxide re equilibration continued to near 530 c or perhaps lower a whole rock rb sr errorchron age for the mealy dykes yielded 1380 54 ma sr1 0 7028 0 0002 which within precision estimates i

historical changes in el nino and la nina characteristics in an ocean reanalysis 1 the variation of el nino southern oscillation enso events from the mid nineteenth century until the beginning of the twenty first century is explored using an ocean reanalysis a comparison of the reanalysis with three sea surface temperature reconstructions shows that the timing of events is similar in all four products however there are important differences in the strength and location of events the difference between the reconstructions is sometimes larger than the difference between the reanalysis and a given reconstruction these differences are larger in the first half of the record a period for which there are relatively sparse observations the reanalysis is used to explore decadal variability and trends in the frequency duration and propagation direction of enso events there is considerable decadal variability of these enso characteristics with the time between events ranging from several months to ten years and the duration of enso varying from 5 to 27 months as has been previously shown for the strength and location of enso there is little overall trend in the characteristics having a three dimensional representation of the ocean from the reanalysis allows exploration of subsurface changes during enso an analysis of subsurface anomalies shows that during enso events the subsurface anomalies are highly correlated with the strength of surface anomalies over the 140 year period overall there is no evidence that there are changes in the strength frequency duration location or direction of propagation of el nino and la nina anomalies caused by global warming during the period from 1871 to 2008

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

asymmetry in summertime atmospheric circulation anomalies over the northwest pacific during decaying phase of el nino and la nina the present study has revealed the asymmetric characteristics of summertime atmospheric circulation anomalies over the indo pacific for el nino and la nina as well as the possible mechanism during the summer when el nino has dissipated there are basin wide warming over the tropical indian ocean tio and cooling over the equatorial central and eastern pacific cep the northwest pacific nwp anticyclone is maintained by a combined effect of the tio warming and equatorial cep cooling the impact of tio warming is via the kelvin wave induced divergence mechanism and the effect of cep cooling is by stimulating a rossby wave response to its northwest correspondingly there are lower upper level convergence divergence over the tio and divergence convergence over the nwp the tropical atmospheric waves and large scale circulation anomalies could couple together and maintain the anticyclone however for la nina there are easterly wind anomalies over the equatorial western pacific and the anomalous nwp cyclone nwpc is weak and shifts northwestward which are largely different from el nino the equatorial cep cooling plays a dominant role in the maintenance of nwpc the negative rainfall anomalies induced by cep cooling force the anticyclonic wind anomalies over the wp as a rossby wave response which further cause the lower upper level convergence divergence over the mc and nwp the resultant convergence leads to the enhanced convection there inducing the nwpc as a rossby wave response besides the equatorial easterly wind anomalies trigger the upwelling oceanic kelvin wave and maintain the cep cooling as the bjerknes feedback

structural evidence and rbsr 39 40ar mica ages relationships for the existence of an hercynian deep crustal shear zone in grande kabylie algeria and its alpine reworking abstract in this paper the hercynian age of the deep crustal shear zone of grande kabylie is determined alpine and hercynian events in the crystallophyllian basement of northeast algeria are separated from field relations and geochronological data obtained with two radiometric systems evidence is presented to show that the blastomylonitic shear belt cutting the crystalline basement of grande kabylie is hercynian in age and that the medium to high grade metamorphism of algiers massif must be older than 243 5 ma the sidi ali bou nab sabn granite dated at 271 12 ma is seen to contain enclaves of mylonitic rocks and is itself affected by a second phase of shearing that appears to be synchronous with emplacement the latest phase of shearing has influenced the granite whole rock systems by increasing their rb sr ratios whilst preserving the alignment of points around a reference isochron of 271 12 m a the influence of eo alpine events is restricted to the opening of k ar muscovite and rb sr biotite systems ages scattered between 25 and 90 ma whereas rb sr muscovite ages show little or no evidence for rejuvenation with ages around 250 ma the rb sr mineral dates presented here along with previously published 39 40 ar step heating age data can be interpreted in the light of structural and metamorphic evidence which shows that pre sabn shearing occurred at temperatures around 650 c and that syn sabn metamorphism and deformation occurred at a temperature between 500 and 550 c it would appear that post hercynian thermal events in the grande kabylie shear zone were no more intense than 300 500 c

orogeny and metamorphism a model for deformation and pressure temperature time paths with applications to the central and southern appalachians a model is presented for deformation uplift and exhumation in convergent orogens based on the following premises 1 foreland basin subsidence monitors the distribution in time and space of overthrust loads added to an orogen 2 the presence of an inherited rifted margin plays an important role in the subsequent history of an orogen by forming a basement ramp or buttress that must be surmounted in order for thrusts to advance on the craton on the seaward side of this transition up to 20 km of overthrusts can be accumulated without creating topography 3 critical shape theory can be applied to orogens as a whole allowing predictions to be made concerning dynamic balance between mass addition and loss uplift exhumation and growth of topography and 4 pressure temperature time p t t data can be used to reconstruct particle paths within the deforming orogen three states of overthrust orogens can be defined based on the relative rates of mass loss and mass addition as monitored by the foreland rapid exhumation of metamorphic terranes is most likely in the steady state where erosion balances accretion a constructive state where mass addition is greater than mass loss results in crustal thickening and initially little exhumation a destructive state where mass loss outweighs mass addition results in slow exhumation or subsidence of metamorphic rocks in the orogen depending on whether mass is removed by erosion or by extension p t t data on peak metamorphism pluton emplacement uplift exhumation and cooling can be used in conjunction with data from the foreland to distinguish among these various states the topography and strength of the inherited rifted margin play an important role in localizing zones of exhumation and uplift within the orogen application of this model to the central and southern appalachians suggests that during the constructive phases of the taconian and acadian orogenies overthrust loads accumulated mainly on the seaward side of the ocean continent transition as marked by the bouguer gravity gradient between the acadian and alleghanian orogenies the appalachian orogen was probably in a steady state with uplift and exhumation of rocks in the orogen but little subsidence of the foreland or advance of thrusts toward the craton the constructive stage of the alleghanian orogeny achieved the critical topography necessary to drive crystalline thrust sheets over the craton this resulted in widespread uplift and westward transport of older metamorphic rocks post orogenic unroofing of the southern appalachians is compatible with the predictions of flexural models the post orogenic unroofing history of the central appalachians and ouachitas probably reflects mesozoic extension in these areas

on the origin of high alumina arc basalt and the mechanics of melt extraction most models of high alumina arc basalt petrogenesis rely heavily on the supposition that the abundances of certain trace elements in particular the relatively unfractionated rare earth element ree patterns and the unusually high concentrations of k rb sr and ba are incompatible with a garnet bearing subducted oceanic crustal quartz eclogite source rock we have carefully examined this apparently unequivocal evidence in light of recent progress on the physics of melt extraction and the heat transfer and mechanics of magma ascent the weakest element of all trace element models involving a quartz eclogite source is the assumption that the element concentrations are fixed at the source and only later modified in the near surface environment we expand on such models by monitoring the concentrations of r ee and major and trace elements during initial melting ascent and extraction of magma this is done by combining calculated cooling curves for ascending magmatic bodies with high pressure phase equilibria the amount that each phase contributes to the melt is monitored along with the composition of the melt and residual solids with quartz eclogite initial melting initiates gravitational instability of the entire source material melt plus solids before melt extraction can occur during ascent of this mush melting increases until the solids can be repacked to free the melt this extraction takes place some 15 20 km above the slab after about 50 per cent melting at which point the melt has a pattern of ree and other trace element concentrations almost identical to those observed in high alumina arc basalts assuming an initial composition equivalent to altered oceanic crust plus 5 per cent pelagic sediment sr abundances are the only ones which are not well matched by this process the major element concentrations of the extracted melt also closely match those of high alumina arc basalt a similar but less detailed evaluation of both fertile and depleted peridotite source rocks yields good agreement for the ree and other trace element concentrations assuming a lree enriched source rock strongly enriched in k rb sr and ba ni cr and co abundances are satisfied only through substantial low pressure fractionation of mafic phases in particular olivine though not rigorously tested such a process may be compatible with the observed major element concentrations of high alumina basalt however the experimentally verified fact that high alumina basalts could never have been in equilibrium with either an olivine beari ng magma or source rock eliminates this possibility altogether thus the simultaneous consideration of the mechanics of ascent and melt extraction along with phase equilibria clearly shows that partial melting of quartz eclogite best satisfies the chemical constraints of major trace and ree characteristics of high alumina arc basalts

asymmetric evolution of el nino and la nina the recharge discharge processes and role of the off equatorial sea surface height anomaly observed oceanic and atmospheric anomalies in the tropical pacific are analyzed to understand the symmetric and asymmetric characteristics between el nino and la nina evolutions it is noted that the evolutions are largely symmetric for el nino and la nina prior to and in their mature phase but become asymmetric afterwards it is further demonstrated that this asymmetry is due to the fact that on average the discharge process associated with el nino is stronger than the recharge counterpart associated with la nina the symmetric and asymmetric evolution for different phases of el nino southern oscillation enso is consistent with the associated recharge and discharge processes that are linked with the evolution of anomalous ocean surface current and gradient of sea surface height anomalies sshas it is suggested that the evolution of the meridional gradient of sshas in the central and eastern equatorial pacific is different between el nino and la nina years due to relatively different rates of the ssha changes on and off the equator during the decay of a warm event the equatorial ssha quickly switches from positive to negative meanwhile the off equator areas are occupied by positive sshas such changes on the equator and in the off equatorial regions make the concavity of the meridional ssha favorable for growth and persistence of westward surface zonal current anomaly in the equatorial pacific then for the enso phase transition during the decay of a cold event the slow decrease of the negative ssha on the equator combined with the disappearance of the negative ssha in the off equatorial regions makes the meridional concavity reverse easily and is unfavorable for the steady growth of the eastward surface zonal current anomaly and for the phase transition thus the asymmetric evolution of enso is associated with both the atmosphere and ocean anomalies on the equator and off the equator