differences in atmospheric circulation between the development of weak and strong warm events in the southern oscillation abstract in this study temporal and spatial aspects of el nino warm event development are explored by comparing composite sequences of sea level pressure slp surface wind and sea surface temperature sst anomalies leading into strong and weak events el nino strength is found to be related to the magnitude and spatial extent of large scale slp anomalies that move in a low frequency mode in association with this it is also intricately linked to the amplitude and wavelength of the rossby waves in the southern midlatitudes the primary signature of the southern oscillation is a more pronounced standing wave of pressure anomalies between southeastern australia and the central south pacific leading into stronger events a strong reversal in the strength of the annual cycle between these two regions causes a stronger weaker slp gradient that drives southwesterly northwesterly wind stress forcing toward away from the western equatorial pacific in austral winter spring of year 0 1 thus pressur

western pacific interannual variability associated with the el nino southern oscillation observations of sea surface temperature sst sea level pressure slp surface wind and outgoing longwave radiation olr show that the el nino southern oscillation enso displays western pacific anomaly patterns in addition to eastern pacific anomaly patterns during the warm phase of enso warm sst and low slp anomalies in the equatorial eastern pacific and low olr anomalies in the equatorial central pacific are accompanied by cold sst and high slp anomalies in the off equatorial western pacific and high olr anomalies in the off equatorial far western pacific also while the zonal wind anomalies over the equatorial central pacific are westerly those over the equatorial far western pacific are easterly the nearly out of phase behavior between the eastern and western tropical pacific is also observed during the cold phase of enso but with anomalies of opposite sign these western pacific interannual anomaly patterns are robust features of enso independent of data sets it is argued that equatorial easterly westerly wind anomalies over the far western pacific during the warm cold phase of enso are initiated by off equatorial western pacific cold warm sst anomalies and that these winds are important for the evolution of enso an atmosphere model is employed to demonstrate that small off equatorial western pacific cold warm sst anomalies compared to those in the east are sufficient to produce equatorial easterly westerly wind anomalies as observed over the far western pacific the coupled ocean atmosphere model of zebiak and cane is then modified to investigate the evolution of the western pacific interannual anomaly patterns in a coupled ocean atmosphere system by including a meridional structure to the subsurface temperature parameterization in the western pacific the modified model produces both western and eastern pacific interannual anomaly patterns

about the role of westerly wind events in the possible development of an el nino in 2014 similarities between early 1997 and 2014 has prompted climate scientists to wonder if an el nino matching the 1997 el nino of the century could develop in 2014 until april 2014 the equatorial pacific exhibited positive heat content anomalies along with an eastward warm pool displacement similar to those found during the onset of strong el nino events yet in july 2014 the warm pool had retreated back to its climatological positions and equatorial temperature anomalies were much weaker than in mid 1997 dedicated oceanic simulations reveal that these weak interannual anomalies can be attributed to differences in westerly wind event wwe sequences in contrast with 1997 the lack of wwes from april to june significantly limited the growth of eastern pacific anomalies and the eastward warm pool displacement in 2014 with the absence of additional wwe activity prospects for a mature el nino in late 2014 are fading

rectification of the madden julian oscillation into the enso cycle an ocean general circulation model forced with idealized purely oscillating wind stresses over the western equatorial pacific similar to those observed during the madden julian oscillation mjo developed rectified low frequency anomalies in sst and zonal currents compared to a run in which the forcing was climatological the rectification in sst resulted from increased evaporation under stronger than normal winds of either sign from correlated intraseasonal oscillations in both vertical temperature gradient and upwelling speed forced by the winds and from zonal advection due to nonlinearly generated equatorial currents the net rectified signature produced by the mjo like wind stresses was sst cooling about 0 48c in the west pacific and warming about 0 18c in the central pacific tending to flatten the background zonal sst gradient it is hypothesized that in a coupled system such a pattern of sst anomalies would spawn additional westerly wind anomalies as a result of sst induced changes in the low level zonal pressure gradient this was tested in an intermediate coupled

mechanisms of the 1997 1998 el nino la nina as inferred from space based observations 1 the intensity of the 1997 el nino and the 8 c sudden drop in sea surface temperature sst around 0 130 w during the turn into la nina in 1998 were a surprise to the scientific community this succession of warm and cold events was observed from start to finish with a comprehensive set of remotely sensed and in situ observations in this study we employ space based observations to demonstrate for the first time their maturity in capturing the preconditioning onset evolution and decay of the 1997 el nino and its transition into the 1998 la nina an accumulation of warm water in the west and equatorial wave reflection on the western ocean boundary appeared favorable for the development of el nino however the action of a series of westerly wind bursts from december 1996 to june 1997 notably in march 1997 was instrumental in setting up this huge el nino the westerly wind bursts excited equatorial downwelling kelvin waves and advected the eastern edge of the warm pool eastward which triggered a distinct warming over the central and eastern parts of the equatorial basin once these warmed regions joined the coupling between the sst and surface winds was fully effective and el nino reached its mature phase by that time much of the warm waters of the western equatorial pacific was transferred toward the east by surface eastward currents the demise of el nino and its turn into la nina in spring 1998 were due to the arrival in the east of various interrelated phenomena upwelling was brought from the west by favorable off equatorial wind stress curl and equatorial kelvin waves generated by easterly winds and wave reflection on the western ocean boundary additional upwelling was brought from the east by equatorial rossby waves generated by westerly winds these various upwelling signals were added to the general uplifting of the thermocline because of the slow discharge of the upper layer of the equatorial basin by diverging surface currents a series of equatorial kelvin and rossby waves characterized by upwelling and opposite surface currents led to the breakup of the warm waters the surfacing of the thermocline and the drastic drop in sst in may 1998 around 0 130 w with the arrival of cold water in the east the easterly winds expanded from the west and la nina turned into a growing mode this view of the 1997 1998 el nino la nina afforded from space enables the testing of various el nino theories

brazilian structural provinces an introduction abstract the territory of brazil coincides almost entirely with the south american platform the crystalline core of the continent its basement is composed of ancient metamorphic and igneous rocks and it has not suffered any tectonic regeneration since the beginning of the phanerozoic sedimentary rocks with almost horizontal bedding cover this crystalline basement this latter shows ages as old as early precambrian although ages between 500 and 1000 m y are conspicuously frequent the cratonic areas became consolidated more than 1700 m y ago whereas the fold belts formed essentially between 500 and 1700 m y ago the sedimentary cover accumulated from the early silurian in three large intracratonic basins until the platform became completely stabilized a late jurassic to early cretaceous reactivation caused by the break up of the ancient gondwana continent created another basin sequence chiefly along the atlantic continental margin based on the nature of the crystalline basement rocks and the sedimentary cover ten structural provinces can be distinguished 1 rio branco province in the north of the country occupied by the guyana shield and still only poorly known with an important fold belt developed during the so called transamazonian cycle 2000 200m y with high grade metamorphic rocks and only slight influence of later events 2 tapajos province in central brazil corresponding to the amazonas or guaporecraton showing chiefly precambrian crystalline rocks and behaving as an cratonic area during the phanerozoic 3 sa o francisco province located on the atlantic shield with its basement covered by rocks of different ages chiefly affected by the brasiliano cycle between 1000 and 500 m y and constituting another cratonic area 4 tocantins province between the amazonas and sa o francisco cratons with the oldest rocks in its centre ages over 2600 m y and at the eastern and western borders metamorphic sequences of various fold belts and almost no phanerozoic deposits 5 mantiqueira province located along the southern part of the atlantic coast affected chiefly by the brasiliano folding cycle 6 borborema province in the northeast brazilian fold belt affected by the brasiliano cycle in a very complex way and with important faulted zones it was reactivated in phanerozoic times when also sedimentary covers accumulated 7 amazonas province represented by the amazonas sedimentary basin syneclise and subdivided into four parts by three important arcs 8 parnaiba province coinciding with the piauf maranha o syneclise and filled with a rather thick sedimentary sequence 9 paranaprovince the sedimentary basin of southern brazil in which the well known late paleozoic glaciation features are found and which possesses an extensive cover of basaltic rocks of late jurassic to early cretaceous age 10 coastal province and continental margin the youngest structural unit developed during the separation of the continent and represented by rift valleys and coastal basins filled with mesozoic cenozoic deposits of various kinds

strike slip tectonics and granite petrogenesis transpression is a process that thickens the crust and therefore in obliquely convergent orogens as in normally convergent orogens there is the potential to generate granitic melts individual transcurrent shear zones may not only control the ascent paths siting and emplacement mechanisms of plutons but they may also cause the genesis of the granitoids themselves two contrasting situations are examined in the hercynian shear zones of iberia thickening together with hydrous fluxing along shear zones created intracrustal wet melting of fertile gondwanan sediments to produce syntectonic granites in the northern part of the british caledonides the association of compositionally expanded granitoids with a major mantle component and transcurrent shear zones may be explained by melting of continental crust at the lower limits of crustal transpressional faults detaching into the moho

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

el nino phase dependent high frequency variability in western equatorial pacific the intensities of high frequency hf variability with period less than 90 days at different phases of el nino events were investigated through observational data analysis a large asymmetry in the hf variability intensity between the developing phase and decaying phase i e pre peak stage versus post peak stage of eastern pacific ep el nino is revealed while the amplitude and spatial pattern of the sea surface temperature anomaly during these two stages are almost same the diagnosis shows that the asymmetry is significant not only on intraseasonal time scale 20 90 days but also on synoptic time scale less than 20 days the anatomy analysis further unveils that the asymmetric synoptic variability between the two episodes arises from the asymmetric intensities of the equatorial rossby and mixed rossby gravity mrg waves we suggest that the stronger vertical easterly wind shear in the pre peak stage than that in the post peak stage plays a vital role in causing the stronger synoptic equatorial rossby and mrg waves in the pre peak stage meanwhile the drier atmosphere and more descending motion in the post peak stage contribute to the weakened intraseasonal and synoptic variabilities in that stage the aforementioned weakened easterly wind shear drier atmosphere and more descending motion in the post peak stage can be traced back to the occurrence of the anomalous anticyclone circulation over the western north pacific since the decaying phase of el nino the essential role of large scale environmental conditions in modulating the hf variability during the two episodes is further confirmed by modeling experiments

el nino southern oscillation related ocean atmosphere coupling in the western equatorial pacific using 43 years of comprehensive ocean atmosphere data set and related data for the period 1950 1992 an examination is made into the regional dependence of ocean atmosphere coupling in relation to the el nino southern oscillation enso the cross correlation between sea surface temperature sst and sea level pressure slp anomalies over the global tropics shows two patterns of significant negative correlation consistent with a local hydrostatic response of slp to sst 1 the eastern pacific where the correlation is symmetric about and largest on the equator and 2 the western pacific where symmetric regions of negative correlation are found off the equator separated by a region of positive correlation on the equator anomalies within these two patterns vary out of phase with each other while the slp anomalies on both sides of the basin are of similar magnitude the sst anomalies in the east are much larger than those in the west despite this disparity in the sst anomaly magnitudes between the eastern and western pacific we argue that the ocean atmosphere couplings in the western and west central pacific are important for enso the off equator sst anomalies in the west enhance the slp anomalies there and they appear to initiate easterly wind anomalies over the far western pacific during the peak el nino phase of enso as these easterlies evolve their effect upon the ocean tends to oppose that of the westerly wind anomalies found over the west central pacific these competing effects suggest a mechanism that may contribute to coupled ocean atmosphere system oscillations the west central equatorial pacific the region separating the eastern and western patterns while exhibiting large momentum and heat flux exchanges shows minimum correlation between sst and slp thus neither the sst and slp anomaly magnitudes nor the correlation between them is alone indicative of ocean atmosphere coupling and the regional dependence for such coupling in relation to enso appears to be more complicated than mechanistic interpretations of enso would suggest

the termination of the 1997 98 el nino part ii mechanisms of atmospheric change the mechanisms that drove zonal wind stress x changes in the near equatorial pacific at the end of the extreme 1997 98 el nino event are explored using a global atmospheric general circulation model the analysis focuses on three features of the x evolution between october 1997 and may 1998 that were fundamental in driving the oceanic changes at the end of this el nino event i the southward shift of near date line surface zonal wind stress x anomalies beginning november 1997 ii the disappearance of the easterly x from the eastern equatorial pacific eeqp in february 1998 and iii the reappearance of easterly x in the eeqp in may 1998 it is shown that these wind changes represent the deterministic response of the atmosphere to the observed sea surface temperature sst field resulting from changes in the meridional structure of atmospheric convective anomalies in response to the seasonally phase locked meridional movement of the warmest sst the southward shift of the near date line x anomalies at the end of this el nino event was controlled by the seasonal movement of the warmest sst south of the equator which both directly and through its influence on the atmospheric response to changes in sst anomaly brought the convective anomalies from being centered about the equator to being centered south of the equator the disappearance reappearance of easterly eeqp x has only been evident in extreme el nino events and has been associated with the development northward retreat of an equatorial intertropical convergence zone itcz the disappearance return of eeqp easterly x arises in the agcm as the deterministic response to changes in the sst field tied principally to the changes in climatological sst given time invariant extreme el nino ssta and not to changes in the underlying ssta field the disappearance return of eeqp easterly x in late boreal winter late boreal spring is a characteristic atmospheric response to idealized extreme el nino sst anomalies this suggests that the distinctive termination of the 1997 98 el nino event is that to be expected for extreme el nino events

episodic metamorphism and deformation in low pressure high temperature terranes in many cases low pressure high temperature metamorphism must be the consequence of advective heat transfer e g the ascent of granitic magma whereas such heating mechanisms are necessarily short lived the lifetime of the underlying orogenic processes is likely to be much longer and it is conceivable that during the evolution of an orogen repeated transient heating at shallow crustal levels is caused by episodes of segregation and upward passage of melts generated at deep crustal levels the number and timing of these events would depend on such factors as critical melt segregation volume moho temperature and strain rate evolution we investigate some of the controls on this multiple event superposition using a simple thermomechanical model designed to predict simultaneously the strain rate and the isostatic and thermal evolution of convergent orogenesis subject to a constant driving force an appealing aspect of this formulation is that in contrast to models that have attempted to explain event cyclicity through episodic processes acting on the orogenic boundaries it accounts for the repeated occurrence of events through processes inherent to the orogenic system itself

on the physical interpretation of the lead relation between warm water volume and the el nino southern oscillation the warm water volume wwv a proxy for the equatorial pacific heat content is the most widely used oceanic precursor of the el nino southern oscillation enso the standard interpretation of this lead relation in the context of the recharge oscillator theory is that anomalous easterlies during e g la nina favour a slow recharge of the equatorial band that will later favour a transition to el nino here we demonstrate that wwv only works as the best enso predictor during boreal spring i e during enso onset in both observations and cmip5 models at longer lead times the heat content in the western pacific wwvw is the best enso predictor as initially formulated in the recharge oscillator theory using idealised and realistic experiments with a linear continuously stratified ocean model and a comprehensive wave decomposition method we demonstrate that spring wwv mostly reflects the fast kelvin wave response to wind anomalies early in the year rather than the longer term influence of winds during the previous year wwv is hence not an adequate index of the slow recharge invoked in the recharge oscillator the wwvw evolution before spring is dominated by forced rossby waves with a smaller contribution from the western boundary reflection wwvw can be approximated from the integral of equatorial wind stress over the previous 10 months thus involving a longer term time scale than wwv main time scale 3 months we hence recommend using wwvw rather than wwv as an index for the slow recharge before the spring predictability barrier

granite emplacement in an extensional setting an ams study of the magmatic structures of monte capanne elba italy abstract monte capanne elba is an excellent example of a granite pluton 42 km 2 emplaced 6 m y ago in a well known extensional environment that of the tyrrhenian sea its internal fabric has been studied using the magnitude of magnetic susceptibility and anisotropy measurements at 74 regularly distributed stations susceptibility magnitudes reveal a normal and asymmetrical petrographical zoning in the pluton the magnetic lineations are remarkably well organized mostly of nw se azimuth with slight plunges and always normal to the walls of the late aplitic dykes these lineations are also parallel to the stretching lineations of the immediate country rocks of the pluton in the western and probably deepest part of the pluton a ne sw trending magnetic magmatic lineation is also imprinted the following scenario is proposed for the emplacement of monte capanne during the opening of the tyrrhenian sea an approximately e w trending sinistral transform fault is taken as being responsible for the creation of a pull apart void that permitted upwelling of the magma orientations of the magmatic structures at depth are parallel to the elongation of the feeding zone of this void i e ne sw the very top part of the pluton was sheared parallel to the granite country rock interface i e nw se parallel to the local stretching of the tyrrhenian sea at the time of emplacement

sensitivity of the asian summer monsoon to aspects of sea surface temperature anomalies in the tropical pacific ocean summary the response of both the time of onset and the strength of the asian summer monsoon to regional aspects of the sea surface temperature sst anomalies in the tropical pacific ocean associated with el nifio southern oscillation enso has been investigated through a series of sensitivity experiments with the universities global atmospheric modelling programme ugamp general circulation model ugcm this paper builds on the work of ju and slingo 1995 and on their hypothesis that the relationship between the asian summer monsoon and enso involved the latitudinal position and strength of the tropical convective maximum tcm over indonesia and the west pacific in the preceding spring the inference from their results was that the modulation of the tcm might be associated either with changes in the walker circulation through the influence of the east pacific sst anomalies or with changes in the local hadley circulation associated with the in situ sst anomalies in the west pacific the investigation has focused on the particular contrasting years of 1983 and 1984 the experiments described in this paper are designed to isolate the effects of the principal sst anomalies in the east and central pacific associated with el niiio la nifia from those of opposite sign which develop in the west pacific as a complementary pattern during the mature phase of el nifiola niba the results of the experimentation suggest that at least for the test cases of 1983 and 1984 the modulation of the walker circulation with implied additional subsidence over the eastern hemisphere is the dominant mechanism whereby the asian summer monsoon is weakened during el nifio years however the late onset during el nifio years may also be associated with the complementary cold sst anomalies in the west pacific which delay the northwards transition of the tcm during la nifia the modulation of the walker circulation appears not to be the controlling factor which determines the stronger monsoons the ugcm results suggest that the complementary warm sst anomalies in the west pacific enhance the tcm and it is this in situ response by the tcm that leads to an early onset and stronger monsoon the importance of warm anomalies in the west pacific in the development of a strong monsoon has been investigated further through a case study of the 1994 season the year 1994 was an el nifio year in which the monsoon was unexpectedly active but which was also marked by wanner than normal ssts in the west pacific the sensitivity experiments have also elucidated the role of el nibo in influencing the precursory signature of stronger subtropical westerlies over india and south east asia during the winter and spring preceding weak monsoons the results suggested that the equatorwards shift of the subtropical jet is a remote response to the warm sst anomalies in the central and east pacific associated with el nifio

the trident pacific model part 2 role of long equatorial wave reflection on sea surface temperature anomalies during the 1993 1998 topex poseidon period the present study aims to give a quantitative description of the role played by long equatorial waves on sea surface temperature anomalies during the 1993 1998 topex poseidon period and more specifically during the 1997 1998 el nino using a new pacific ocean model called trident in a companion paper the trident dynamical component was described and validated with observations briefly the model exhibits skill in simulating not only sea level but also surface zonal current variability in the equatorial wave guide here the model thermodynamics are described and validated the thermodynamics of trident consist of one single equation for interannual sea surface temperature anomalies compared to other similar models the introduction in the temperature equation of a term equivalent to a vertical mixing term improves significantly the temperature simulations in the eastern pacific thus the model comparison to interannual sea level zonal current and sea surface temperature anomalies is fairly good over the entire equatorial pacific ocean the model is found to be sensitive to both subsurface variability central and eastern pacific and to zonal current advection especially near the dateline where the data suggest that advection is a first order process for determining sea surface temperature changes the role of long equatorial wave reflection observed in topex poseidon data is studied by either cancelling the eastern boundary or western boundary reflection first at the eastern boundary although the reflected rossby waves were found to act against the warming during the onset phase of the 1997 1998 el nino through zonal advection the major impact of these reflected rossby waves was to reinforce the deepening of the thermocline in the eastern pacific initiated by the impinging kelvin waves therefore all things considered the rossby waves strongly contributed to the warming in 1997 1998 east of 120 w secondly at the western boundary rossby wave reflection acted as suggested by the delayed action oscillator theory the reflected kelvin waves caused shoalling of the thermocline in the central and eastern pacific where they weakened the warm or cold conditions observed in the pacific ocean during the 1997 1998 event specifically they contributed to about a third of the upwelling kelvin wave amplitude propagating in the central pacific the other two thirds of the amplitude were found to be actually wind forced strongly suggesting that during that event easterly wind anomalies in the western pacific played a significant role in the termination of the recent 1997 1998 el nino event and its switch to the la nina period

the trident pacific model part 1 simulating surface ocean currents with a linear model during the 1993 1998 topex poseidon period zonal advection by long equatorial waves has been shown to be an important process in the evolution of sea surface temperature in the central pacific on enso time scales the present study aims at investigating how well an oceanic model whose dynamics are based on long equatorial waves can simulate the large scale surface zonal current variability thus an ocean linear model which can be run with two or three layers is validated against several sets of observations in the pacific ocean topex poseidon sea level tao zonal currents surface current climatology the surface layer mixed layer has a constant depth therefore the layer model is equivalent to considering a shear layer solution and either one or two baroclinic modes it allows evaluation of the impact of adding a second baroclinic mode on the simulation of surface currents this evaluation is done for different friction parametrizations a weak linear rayleigh friction 24 months 1 a strong linear rayleigh friction 6 months 1 and a new parametrization using quadratic friction in the momentum equation only it is shown in all simulations using various rayleigh friction parametrizations that the addition of a second baroclinic mode always improves the simulation of both the sea level and the surface currents especially in the central western pacific in that region there is a reduction of the propagating long rossby waves whose amplitude is much too large when only one baroclinic mode is used despite this reduction the use of a weak friction 24 months 1 always yields results which compare only poorly to observations confirming results from previous studies the use of strong friction 6 months 1 improves the model simulation but surface current variability still remains too large finally the use of quadratic friction as proposed in the present study considerably improves the simulation of zonal currents and its comparison to all data sets this result gives more confidence in the choice of such a simple model to further explore the role of zonal advection by long equatorial waves on enso time scales

the transition from magmatic to high temperature solid state deformation implications from the mount stuart batholith washington criteria for syntectonic emplacement of plutons are commonly ambiguous the strongest single criterion is probably the preservation of a continuous transition from submagmatic to high temperature solidstate deformation this transition is not commonly documented an exception is the mount stuart batholith which displays a variety of syntectonic structures within its sheared northeastern margin including the following 1 s c fabrics that range from submagmatic to high temperature solid state 2 solid state foliation and lineation defined by amphibolite facies assemblages that overprint and are parallel to magmatic foliation and lineation 3 folds of magmatic and solid state foliation that have hinge lines parallel to magmatic and solid state lineation and to equivalent structures in wall rocks 4 dikes that were folded and boudinaged over a wide range of rheological states with boudin necks locally filled by tonalite 5 pegmatite dikes and mineralized joints that are sub perpendicular to magmatic and solid state lineation and 6 submagmatic and high temperature solidstate ductile shear zones we suggest that many plutons emplaced during regional deformation do not preserve evidence for syntectonic deformation because of the transitory nature of the submagmatic state and the obscuring effects of postemplacement deformation syntectonic features are most likely preserved in plutons cooled at slow to moderate rates or in plutons deformed at high strain rates during emplacement the optimum conditions for preservation may occur in plutons emplaced along fault zones in the mid crust such as the mount stuart batholith and in intrusions at deeper levels that were rapidly exhumed and or intruded during the waning stages of regional deformation

shear criteria in granite and migmatite deformed in the magmatic and solid states microstructural criteria for the determination of the sense of shear in rocks homogeneously deformed in the partially melted state are similar to those which apply to solid state deformation sense of shear determination is either direct deduced from the sense of rotation of markers or indirect involving the obliquity between the shear and foliation planes or between the successive foliations imprinted at different stages of progressive deformation this study is a by product of the detailed structural and microstructural investigation of a high grade metamorphic rock pile variscan vosges massif france which underwent subhorizontal shearing during partial melting and further solidification depending on the rock chemistry on the position in the pile and the relative timing of progressive deformation layered migmatites and homogeneous granites were variously deformed in the partially melted and solid states the sense of shear obtained from these rock types using the criteria presented here consistently gives a top to sw direction

the 1997 98 el nino evolution relative to previous el nino events abstract the evolution of the 1997 98 el nino is described using ncep sst and olr data ncep ncar reanalysis sea level pressure slp fields and the florida state university surface wind data from november 1996 to january 1997 the eastern pacific is characterized by equatorial cold sst and high slp anomalies while the western pacific is marked by off equatorial warm sst anomalies and off equatorial anomalous cyclones corresponding to this distribution are high olr anomalies in the equatorial central pacific and low olr anomalies in the off equatorial far western pacific the off equatorial anomalous cyclones in the western pacific are associated with a switch in the equatorial wind anomalies over the western pacific from easterly to westerly these equatorial westerly anomalies then appear to initiate early sst warmings around the date line in january february 1997 and around the far eastern pacific in march 1997 subsequently both the westerly wind and warm sst anomalies along with the low olr ano

magma assisted strain localization in an orogen parallel transcurrent shear zone of southern brazil in a lithospheric scale orogen parallel transcurrent shear zone of the pan african dom feliciano belt of southern brazil two successive generations of magmas an early calc alkaline and a late peraluminous have been emplaced during deformation microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions magmatic deformation is indicated by the coexistence of aligned k feldspar plagioclase micas and or tourmaline with undeformed quartz submagmatic deformation is characterized by strain features such as fractures lattice bending or replacement reactions affecting only the early crystallized phases high temperature solid state deformation is characterized by extensive grain boundary migration in quartz myrmekitic k feldspar replacement and dynamic recrystallization of both k feldspar and plagioclase decreasing temperature during solid state deformation is inferred from changes in quartz crystallographic fabrics decrease in grain size of recrystallized feldspars and lower ti amount in recrystallized biotites final low temperature deformation is characterized by feldspar replacement by micas the geochemical evolution of the synkinematic magmatism from calc alkaline metaluminous granodiorites with intermediate 87sr 86sr initial ratio to peraluminous granites with very high 87sr 86sr initial ratio suggests an early lower crustal source or a mixed mantle crustal source followed by a middle to upper crustal source for the melts shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle but whatever the process initiating partial melting lithospheric transcurrent shear zones may collect melt at different depths because they enhance the vertical permeability of the crust these zones may then act as heat conductors by advection promoting an upward propagation of partial melting in the crust synkinematic granitoids localize most if not all deformation in the studied shear zone the regional continuity and the pervasive character of the magmatic fabric in the various synkinematic granitic bodies consistently displaying similar plane and direction of flow argue for accommodation of large amounts of orogen parallel movement by viscous deformation of these magmas moreover activation of high temperature deformation mechanisms probably allowed a much easier deformation of the hot synkinematic granites than of the colder country rock and consequently contributed significantly to the localization of deformation finally the small extent of the low temperature deformation suggests that the strike slip deformation ended approximately synchronously with the final cooling of the peraluminous granites the evolution of the deformation reflects the strong influence of synkinematic magma emplacement and subsequent cooling on the thermomechanical evolution of the shear zone magma intrusion in an orogen scale transcurrent shear zone deeply modifies the rheological behavior of the continental crust it triggers an efficient thermomechanical softening localized within the fault that may subsist long enough for large displacements to be accommodated therefore the close association of deformation and synkinematic magmatism probably represents an important factor controlling the mechanical response of continental plates in collisional environments

the influence of large ductile shear zones on the emplacement and deformation of the wyangala batholith se australia abstract the wyangala batholith consists of many small s and i type plutons most of which are elongate in a n s direction our studies of this batholith indicate that n s striking magmatic foliations exist in some of the individual plutons but are not strongly developed a few individual plutons show evidence of forceful emplacement but in general most do not intense post emplacement deformation occurs in a series of e directed thrusts that border the eastern edge of individual plutons or the batholith as a whole this thrusting formed gneissic layering mylonites and secondary foliations in the batholith and complex polyphase folding and cleavage development in the wall rocks we suggest that the batholith was emplaced as sheet like bodies possibly along steep reverse faults data presently available indicate that the pre emplacement deformation of the wall rocks is middle silurian that the batholith was emplaced in the late silurian and that post emplacement thrusting is late silurian to early carboniferous finally the close association of batholiths and regions of complex deformation in the lachlan fold belt suggest to us that these elements may represent shallow level equivalents of hollister crawford s surge tectonics geology 14 558 561 1986

tropical pacific sea surface temperature anomalies el nino and equatorial westerly wind events abstract the authors examine global statistical relationships between westerly wind events wwes and sea surface temperature anomaly ssta variability using a compositing technique for the period 1986 98 the authors describe the extent to which equatorial wwes are associated with central and eastern equatorial pacific waveguide warming and with local ssta changes under the wwe their goal is to quantify the extent to which equatorial wwes are fundamental to the onset and maintenance of warm el nino southern oscillation conditions in order to understand the effect of wwes on ssta evolution they begin by examining how ssta changes in the absence of equatorial wwes they find that ssta tends toward mean climate values in the absence of equatorial wwes whether the eastern equatorial pacific has close to normal ssta or warmer than normal ssta the two equatorial wwe types whose main surface wind anomalies are west of the date line are associated with weak local surface cooling the equatorial wwe type t

role of high and low frequency winds and wave reflection in the onset growth and termination of the 1997 1998 el nino the present study aims at studying the role played by high frequency wind variability wave reflection and easterly wind anomalies in the western pacific in the onset growth and termination phases of the 1997 1998 el nino using the trident intermediate coupled model and observations while the anomalous strength of the trade winds in 1996 favored the initiation of a warm event in 1997 via western pacific boundary rossby wave reflection the actual timing of the onset and the amplitude of the event resulted from the large march 1997 wind event once initiated high frequency westerly winds strongly contributed to the rapid growth of the warm event and to the displacement of the eastern edge of the warm pool moreover both easterly and westerly high frequency wind variability in 1997 1998 contributed to the amplitude of the event set the evolution of the warm event and potentially influenced the equatorial pacific conditions at least one year after the el nino event in addition eastern boundary reflection also significantly contributed to the amplitude and duration of the warm event whereas its termination was a combination of various factors reflection of upwelling rossby waves at the western boundary and large easterly wind anomalies observed in the western pacific from november 1997 to early 1998 these factors were sufficient to terminate the event and to switch temperature anomalies from warm to cold to conclude understanding the coupling between the high and low frequency wind variability i e studying enso as a multi scale phenomenon will certainly lead to a better comprehension of the diversity of its behavior and potentially to an improvement of its predictability

modulation of equatorial pacific westerly easterly wind events by the madden julian oscillation and convectively coupled rossby waves synoptic wind events in the equatorial pacific strongly influence the el nino southern oscillation enso evolution this paper characterizes the spatio temporal distribution of easterly ewes and westerly wind events wwes and quantifies their relationship with intraseasonal and interannual large scale climate variability we unambiguously demonstrate that the madden julian oscillation mjo and convectively coupled rossby waves crw modulate both wwes and ewes occurrence probability 86 of wwes occur within convective mjo and or crw phases and 83 of ewes occur within the suppressed phase of mjo and or crw 41 of wwes and 26 of ewes are in particular associated with the combined occurrence of a crw mjo far more than what would be expected from a random distribution 3 wind events embedded within mjo phases also have a stronger impact on the ocean due to a tendency to have a larger amplitude zonal extent and longer duration these findings are robust irrespective of the wind events and mjo crw detection methods while wwes and ewes behave rather symmetrically with respect to mjo crw activity the impact of enso on wind events is asymmetrical the wwes occurrence probability indeed increases when the warm pool is displaced eastward during el nino events an increase that can partly be related to interannual modulation of the mjo crw activity in the western pacific on the other hand the ewes modulation by enso is less robust and strongly depends on the wind event detection method the consequences of these results for enso predictability are discussed

shear zone controlled magma emplacement or magma assisted nucleation of shear zones insights from northeast brazil abstract in the borborema province of northeast brazil neoproterozoic granitoids and large scale transcurrent shear zones are spatially associated suggesting a genetic link between magma bodies and shear zones in some cases magma emplacement was clearly favored by shear zone activity but for several plutons this model is not satisfactory in these plutons pre full crystallization strike slip deformation evidenced by parallelism of magmatic foliations and lineations with the solid state mylonitic fabric and by a transition from magmatic to solid state flow is restricted to the vicinity of the shear zones evidence of shear zone activity prior to magma emplacement is lacking and the magmatic foliation away from the shear zones is in most cases shallowly dipping and concordant with the slightly older gently dipping regional gneissic foliation field and anisotropy of magnetic susceptibility mapping together with petrographic and geochemical studies performed in one of the magmatic complexes of the borborema province have revealed a structure and a magmatic fabric incompatible with the shear zone controlled emplacement model away from the shear zones this complex has retained a stratification inherited from the mixing of crystal poor magmas of contrasting composition and a magmatic fabric characterized by low to moderate dip magmatic foliations bearing a nw trending lineation which contrast with vertical foliations bearing ne or e w trending stretching lineations in the shear zones and indicates that crystallization started prior to shear zone development based on evidence that magma emplacement predated strike slip shearing and on information about the transition from magmatic to solid state deformation observed in the studied plutons we suggest that incompletely solidified plutons within the crust represent rheological heterogeneities that may induce strain localization and favor shear zone nucleation we propose that in the studied cases deformation first concentrated within the plutons where shear zones nucleated and grew subsequently as the solid phase component increased the crystal mush began to behave as a solid and the shear zones propagated into the country rocks

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

influence of westerly wind events stochasticity on el nino amplitude the case of 2014 vs 2015 the weak el nino of 2014 was preceded by anomalously high equatorial pacific warm water volume wwv and strong westerly wind events wwes which typically lead to record breaking el nino like in 1997 and 2015 here we use the cnrm cm5 coupled model to investigate the causes for the stalled el nino in 2014 and the necessary conditions for extreme el ninos this model is ideally suited to study this problem because it simulates all the processes thought to be critical for the onset and development of el nino it captures el nino preconditioning by wwv the wwes characteristics and their deterministic behaviour in response to warm pool displacements our main finding is that despite their deterministic control wwes display a sufficiently strong stochastic component to explain the distinct evolutions of el nino in 2014 and 2015 a 100 member ensemble simulation initialized with early spring equatorial conditions analogous to those observed in 2014 and 2015 demonstrates that early year elevated wwv and strong wwes preclude the occurrence of a la nina but lead to el ninos that span the weak with few wwes to extreme with many wwes range sensitivity experiments confirm that numerous strong wwes shift the el nino distribution toward larger amplitudes with a particular emphasis on summer fall wwes occurrence which result in a five fold increase of the odds for an extreme el nino a long simulation further demonstrates that sustained wwes throughout the year and anomalously high wwv are necessary conditions for extreme el nino to develop in contrast we find no systematic influence of easterly wind events ewes on the el nino amplitude in our model our results demonstrate that the weak amplitude of el nino in 2014 can be explained by wwes stochastic variations without invoking ewes or remote influences from outside the tropical pacific and therefore its peak amplitude was inherently unpredictable at long lead time

granite magma generation ascent and emplacement within a transpressional orogen crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement granites may be transported from sites of generation through the mid crust in dyke like channelways within relatively narrow strike slip shear zones which link to major fault zones in the upper crust extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below the model is based upon observations from the cadomian belt of nw france which exposes sections through middle and upper levels of the late precambrian crust within different elements of the orogen the mechanism provides a favourable alternative to diapirism and explains the common collocation of granites and shear zone fault systems within orogenic belts

eastern equatorial pacific response to three composite westerly wind types it has been suggested recently that episodes of westerly wind near the international date line in the western pacific tend to fall into one of four types three of the types have enough equatorial zonal wind variation to be able to induce an eastern pacific response by forcing equatorial waves in this note we examine the central and eastern pacific waveguide response to idealized representations of these three types of westerly wind episodes using a combination of linear theory and results from an ocean general circulation model the idealized westerly wind types are the c type maximum anomalies centered on the equator the n type maximum anomalies just north of the equator and the s type maximum anomalies just south of the equator the composite c type event excites equatorially trapped kelvin pulses that alter sea surface temperature in the central and eastern pacific warm anomalies caused by the c type episode have approximately equal contributions from a zonal advection of heat by the kelvin pulses and a meridional advection of heat by an altered instability wave field because the center of forcing of the s type event is displaced off of the equator the kelvin pulses excited by the s type episode have smaller amplitude than those of the c type episode even though the maximum wind anomaly is the same in the two cases the s type anomaly also excites weak rossby gravity waves that can propagate into the eastern pacific because the rossby gravity waves are dispersive their amplitude diminishes as the waves propagate into the eastern pacific the n type episode as observed in winds from the western tropical pacific is much weaker and of shorter duration than the c and s types and therefore excites only a very weak eastern pacific response although all types of westerly wind excite a local western pacific response only the c and s type events excite a significant eastern pacific response

a unified oscillator model for the el nino southern oscillation the delayed oscillator the western pacific oscillator the recharge discharge oscillator and the advective reflective oscillator have been proposed to interpret the oscillatory nature of the el nino southern oscillation enso all of these oscillator models assume a positive ocean atmosphere feedback in the equatorial eastern and central pacific the delayed oscillator assumes that the western pacific is an inactive region and wave reflection at the western boundary provides a negative feedback for the coupled system to oscillate the western pacific oscillator emphasizes an active role of the western pacific in enso the recharge discharge oscillator argues that discharge and recharge of equatorial heat content cause the coupled system to oscillate the advective reflective oscillator emphasizes the importance of zonal advection associated with wave reflection at both the western and eastern boundaries motivated by the existence of these different oscillator models a unified oscillator model is formulated and derived from the dynamics and thermodynamics of the coupled ocean atmosphere system consistent with enso anomaly patterns observed in the tropical pacific this oscillator model considers sea surface temperature anomalies in the equatorial eastern pacific zonal wind stress anomalies in both the equatorial central pacific and the equatorial western pacific and thermocline depth anomalies in the off equatorial western pacific if the western pacific wind forced response is neglected thermocline and zonal wind stress anomalies in the western pacific are decoupled from the coupled system and the unified oscillator reduces to the delayed oscillator if wave reflection at the western boundary is neglected the unified oscillator reduces to the western pacific oscillator the mathematical form of the recharge discharge oscillator can also be derived from this unified oscillator most of the physics of the advective reflective oscillator are implicitly included in the unified oscillator and the negative feedback of wave reflection at the eastern boundary is added to the unified oscillator with appropriate model parameters chosen to be consistent with those of previous oscillator models the unified oscillator model oscillates on interannual timescales

role of melt during deformation in the deep crust deformation in the deep crust is strongly influenced by the presence of melt injected melt or magma weakens the crust because strain will tend to localize where melt is present the amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate for plutons that intrude into rocks which are near the solidus temperature of the melt crystallization times can be quite long 1myr partial melting of deep crustal rocks can lead to melt enhanced embrittlement this occurs because the volume change for most melting reactions is positive therefore when the rate of melt production outpaces the rate at which melt can leave the system the melt pressure increases eventually the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the central gneiss belt canada this suggests that melt enhanced embrittlement occurred in these rocks an expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived assuming that migmatite has a small tensile strength differential stresses are 20 mpa in migmatitic rocks at the time melt enhanced embrittlement occurs the occurrence of melt enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting furthermore repeated episodes of melt enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains

a tectonic model for the emplacement of the main donegal granite nw ireland the main donegal granite is shown to lie in a major late stage ne sw trending transcurrent sinistral shear zone in the caledonides of nw ireland the zone which is bent both laterally and upwards around the pluton has displacements which diminish sw along its length from a maximum of approximately 20 km at the ne end of the pluton the granite has also been deformed by this sinistral shear but it has a strain component of its own the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone strain variations between granite and wall rock and an early plagioclase fabric associated with the petrographic banding of the granite suggest that intrusion and deformation were more or less synchronous at around 400 ma it is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend split lengthwise and progressively create an internal low pressure zone into which the main granite was emplaced the wide variety of emplacement styles of the other radiometrically synchronous plutons of the batholith can be attributed to the progressive development of the shear zone thorr and fanad in tension between the zone and a complimentary structure to the n ardara and toories in local compression at the shear zone termination rosses in tension on the outer arc of the bending zone and trawenagh bay as displaced main granite magma in a similar tensional setting during the final stages of deformation

strain transfer at continental scale from a transcurrent shear zone to a transpressional fold belt the patos serido system northeastern brazil during the brasiliano pan african orogeny a complex continental scale pattern of east west transcurrent shear zones and northeast trending fold belts formed in the northern and central borborema province of northeastern brazil the east west shear zones have been usually regarded as slightly younger features but the study of the most spectacular case of intersection between these two structures the patos shear zone and the serido transpressional belt leads to a different tectonic model satellite imagery and structural petro logical and geophysical data support the interpretation that these structures 1 are in structural continuity and 2 formed simultaneously under amphibolite facies metamorphic conditions that led to partial melting this suggests a model of strain transfer at the scale of the orogen at the eastern end of the patos east west dextral shear zone the strain that accommodated the relative motion of the northern block was transferred to the northeast trending serido belt where it resulted in folding strike slip faulting and stretching parallel to the strike of the belt

the mortagne granite pluton france emplaced by pull apart along a shear zone structural and gravimetric arguments and regional implication the emplacement mechanism and kinematics and the 3 d geometry of the variscan granite pluton of mortagne are interpreted using systematic measurements of the granite structure allied with micro structural observations from a detailed gravimetric study it is proposed that magma infilled a pull apart structure which formed along a jog of a northwest southeast trending sinistral zone of shear a second episode of shearing under a dextral regime and independent of emplacement was responsible for perigranitic tectonites these successive transcurrent opposite movements already documented for variscan times in western france are discussed concerning the age of the mortagne pluton 313 15 m y

a western pacific oscillator paradigm for the el nino southern oscillation a data based hypothesis is presented on the mechanism of the el nino southern oscillation enso a major determinant of interannual global climate variability the hypothesis emphasizes the importance of off equator sea surface temperature and sea level pressure variations west of the dateline for initiating equatorial easterly winds over the far western pacific these winds compete with westerly winds over the equatorial central pacific enabling the coupled ocean atmosphere system to oscillate consistent with this hypothesis an analogical oscillator model is constructed that produces enso like oscillations the proposed mechanism differs from the delayed oscillator paradigm in that wave reflection at the western boundary is not a necessary condition for the coupled ocean atmosphere system to oscillate

the march 1997 westerly wind event and the onset of the 1997 98 el nino understanding the role of the atmospheric response in a previous study the effect of the march 1997 westerly wind event wwe on the evolution of the tropical pacific ocean was studied using an ocean general circulation model gcm the response was characterized by i a cooling of the far western pacific 0 88c ii a rapid eastward displacement of the warm pool 2000 km in a month and iii a weak warming of the central eastern pacific along the path of the oceanic kelvin wave excited by the wwe 0 58c in this study the atmospheric response to these aspects of the sea surface temperature sst response are investigated using an atmospheric gcm forced with the sst anomalies from the ocean only experiments the results have demonstrated that the three aspects of the sst anomaly field generated by the wwe

the great tonalite sill emplacement into a contractional shear zone and implications for late cretaceous to early eocene tectonics in southeastern alaska and british columbia the late cretaceous to early tertiary great tonalite sill of southeast alaska and british columbia is a very long 1 000 km and thin 25 km orogen parallel composite batholith which lies between the insular superter rane including the alexander and wrangellia terranes and the intermontane superterrane including the stikine and cache creek terranes the batholith is delineated by many steep sheet like plutons which are dominated by northwest southeast striking concordant fabrics with steep lineations that formed during deformation in a country rock shear zone prior to the complete crystallization of the magmas deformation in this shear zone is dominated by northeast southwest directed contraction orthogonal to the orogenic strike associated with a component of northeast over southwest high angle shear the steep multiple dike like nature of the body and its emplacement during orogenic contraction imply that ascent and emplacement have been achieved by dike wedging mechanisms along the deep reaching shear zone the remarkable narrowness of the great tonalite sill is probably the result of melting at the base of a very localized zone of thickened crust produced by the associated narrow contractional shear zone extending along the orogen length such a shear zone of late cretaceous to early tertiary age lying along 800 km of the possible boundary between the insular and intermontane superterranes implies that it may represent the actual boundary between them if this hypothesis is correct it implies that the large scale tectonic regime during emplacement of the great tonalite sill was predominantly orthogonal and not obliquely dextral as has been indicated from paleomagnetic data

abrupt termination of the 1997 98 el nino in response to a madden julian oscillation the role of the madden julian oscillation a global atmospheric wave in the tropics that is associated with convective activity and propagates eastwards with a period of about 30 60 days refs 1 2 in triggering el nino events has been discussed before3 4 5 6 7 8 but its possible connection with a termination of el nino has yet to be investigated despite the difficulty in explaining the timing of el nino terminations by the basic wind induced oceanic wave processes9 10 for the extreme 1997 98 event the mechanism of both onset and termination have been investigated3 but the reason for the abruptness of the termination has yet to be resolved here we present global data of precipitation sea surface temperatures and wind speeds that show a precipitation system associated with an exceptionally strong madden julian oscillation travelling around the equator in may 1998 the propagation of this atmospheric system was associated with an abrupt intensification of the easterly trade winds over the eastern equatorial pacific ocean combined with the already shallow equatorial thermocline in the central and eastern pacific ocean at that time3 these strong winds provided the triggering mechanism for the observed accelerated ending of the 1997 98 el nino event

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

triggering of el nino by westerly wind events in a coupled general circulation model two ten members ensemble experiments using a coupled ocean atmosphere general circulation model are performed to study the dynamical response to a strong westerly wind event wwe when the tropical pacific has initial conditions favourable to the development of a warm event in the reference ensemble cref no wind perturbation is introduced whereas a strong westerly wind event anomaly is introduced in boreal winter over the western pacific in the perturbed ensemble cwwe our results demonstrate that an intense wwe is capable of establishing the conditions under which a strong el nino event can occur first it generates a strong downwelling kelvin wave that generates a positive sea surface temperature sst anomaly in the central eastern pacific amplified through a coupled ocean atmosphere interaction this anomaly can be as large as 2 5 c 60 days after the wwe secondly this wwe also initiates an eastward displacement of the warm pool that promotes the occurrence of subsequent wwes in the following months these events reinforce the initial warming through the generation of additional kelvin waves and generate intense surface jets at the eastern edge of the warm pool that act to further shift warm waters eastward the use of a ten members ensemble however reveals substantial differences in the coupled response to a wwe whereas four members of cwwe ensemble develop into intense el nino warming as described above four others display a moderate warming and two remains in neutral conditions this diversity between the members appears to be due to the internal atmospheric variability during and following the inserted wwe in the four moderate warm cases the warm pool is initially shifted eastward following the inserted wwe but the subsequent weak wwe activity when compared to the strong warming cases prevents to further shift the warm pool eastwards the seasonal strengthening of trade winds in june july can therefore act to shift warm waters back into the western pacific reducing the central eastern pacific warming this strong sensitivity of the coupled response to wwes may therefore limit the predictability of el nino events as the high frequency wind variability over the warm pool region remains largely unpredictable even at short time lead

magnetic and magmatic structures of the emas granodioritic pluton cachoeirinha belt ne brazil relationships with pan african strike slip fault systems abstract the emas granodiorite was intruded during the brasiliano pan african orogeny into the metapelites of the cachoeirinha belt ne brazil this pluton was chosen for a petrofabric study of magmatic emplacement structures using magnetic anisotropy because of its conspicuous position in the junction area between the large e w trending patos shear zone and the ne sw trending cachoeira da mina strike slip fault the magnetic behavior of this calc alkaline granite is dominated by paramagnetic minerals which is optimal for the application of the anisotropy of magnetic susceptibility technique used for this study almost all microstructures correspond to the magmatic state so the measured magnetic lineations and foliations may be interpreted respectively as directions and planes of magmatic flow these magnetic magmatic lineations and foliations are dominantly n s and ne sw oriented and are gently to moderately dipping the anisotropy of magnetic susceptibility ratios range from 1 to 5 4 most of these values corresponding to magmatic alignment the lowest ratios are located chiefly in the centre of the pluton and the highest on the northern and western margins from these data we propose that the emplacement of the emas pluton was controlled by a ne sw trending left lateral strike slip zone parallel to the cachoeira da mina fault giving rise to openings in the metapelitic country rocks infilled by two succesive magmas the principal result of this study is the unexpected independence between the emplacement of the emas pluton and the functioning of the patos dextral shear zone

revisiting the 1872 owens valley california earthquake the 26 march 1872 owens valley earthquake is among the largest historical earthquakes in california the felt area and maximum fault displacements have long been regarded as comparable to if not greater than those of the great san andreas fault earthquakes of 1857 and 1906 but mapped surface ruptures of the latter two events were 2 3 times longer than that inferred for the 1872 rupture the preferred magnitude estimate of the owens valley earthquake has thus been 7 4 based largely on the geological evidence reinterpreting macroseismic accounts of the owens valley earthquake we infer generally lower intensity values than those estimated in earlier studies nonetheless as recognized in the early twentieth century the effects of this earthquake were still generally more dramatic at regional distances than the macroseismic effects from the 1906 earthquake with light damage to masonry buildings at nearest fault distances as large as 400 km macroseismic observations thus suggest a magnitude greater than that of the 1906 san francisco earthquake which appears to be at odds with geological observations however while the mapped rupture length of the owens valley earthquake is relatively low the average slip was high the surface rupture was also complex and extended over multiple fault segments it was first mapped in detail over a century after the earthquake occurred and recent evidence suggests it might have been longer than earlier studies indicated our preferred magnitude estimate is mw 7 8 7 9 values that we show are consistent with the geological observations the results of our study suggest that either the owens valley earthquake was larger than the 1906 san francisco earthquake or that by virtue of source properties and or propagation effects it produced systematically higher ground motions at regional distances the latter possibility implies that some large earthquakes in california will generate significantly larger ground motions than san andreas fault events of comparable magnitude

the pombal granite pluton magnetic fabric emplacement and relationships with the brasiliano strike slip setting of ne brazil paraiba state abstract the pombal pluton 500 km 2 a suite of diorite syenite and porphyritic granite bodies is here used to constrain kinematics of brasiliano age tectonic episodes in northeast brazil the pluton intrudes high grade to migmatitic gneiss forming the western basement of the serido belt and is located at the intersection between two sets of continental scale dextral strike slip shear zones the northern set of shear zone strikes ne sw and branches southwards into the e w patos mega shear zone a detailed microstructural and low field magnetic susceptibility study was performed to unravel the relationships between solid state deformation in the country rocks and magma emplacement porphyritic granite and syenite have quite high magnetic susceptibilities 10 3 10 2 si units indicative of magnetite as the principal carrier of susceptibility the magnetic fabric is remarkably homogeneous in orientation throughout the pluton it is characterized by a shape preferred alignment of magnetite itself parallel to the shape fabric of mainly biotite amphibole i e to the magmatic fabric even close to the contact with the high temperature mylonites of the patos shear zone south of pombal no imprint of the e w trending structures is observed in the fabrics of either the granite or the host rocks granite emplacement and its internal fabric development is concluded to be independent of the movement of the patos shear zone in the southwestern border of the pluton a low dip foliation bearing a ne sw striking lineation is shared in both the magmatic fabric of the pluton and the solid state fabric farther to the north approaching the ne sw strike slip shear zone the magmatic fabric is characterized by a steeply dipping ne striking foliation carrying a subhorizontal lineation transition from low to steep dips of the planar fabrics is progressive two models are proposed for emplacement of the pombal pluton one considers magma injection during an early episode of tangential tectonics responsible for the gently dipping foliations evolving later to strike slip deformation the other model considers that the pluton was emplaced in a pull apart domain developed in the overlapping sector of a right hand en echelon system of a dextral shear zone compatibility of these models with the tectonic evolution of the serido belt is discussed

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others

initiation and propagation of shear zones in a heterogeneous continental lithosphere continental plates represent rheologically heterogeneous media in which complex finite strain fields may develop due to interaction of plate tectonic processes with intraplate heterogeneities such a deformation pattern is displayed by the borborema shear zone system in northeastern brazil it involves continental scale curvilinear e w trending right lateral transcurrent shear zones that branch off from a major ne trending right lateral strike slip deformation zone formed at the northern termination of the sao francisco craton and that finally terminate in transpressive metasedimentary belts we suggest that this strain field results from the compressional deformation of a highly heterogeneous continental lithosphere composed of a stiff domain craton and rheologically weaker domains basins the effect of a low viscosity domain on the deformation of a continental plate and in particular the perturbation induced by this domain on the development of a shear zone formed at the termination of a stiff block were investigated using numerical modeling the low strength domain induces an enhanced strain localization and the geometry of the shear zone is significantly modified it is either split forming a branched shear zone system in which one branch maintains its original orientation while the other rotates toward the low viscosity domain or completely rotated toward the weak block the perturbation of the finite strain field depends on the ability of the weak domain to accommodate deformation which is controlled by its initial viscosity contrast relative to the surrounding lithosphere its orientation relative to the convergence direction and its distance from the shear zone initiated at the termination of the stiff block the interaction between imposed boundary conditions tectonic forces and plate geometry and the internal structure of the plate may give rise to highly heterogeneous strain fields as exhibited by the borborema shear zone system in which intraplate rheological heterogeneities induce the development of branched or sinuous shear zones a heterogeneous continental plate subjected to a normal convergence may therefore display significant lateral variations in strain intensity with shear zones bordering nearly undeformed blocks and in deformation regimes and vertical strains that would result in contrasting metamorphic and uplift histories

contrasting intraseasonal variations of the equatorial pacific ocean between the 1997 1998 and 2015 2016 el nino events oceanic intraseasonal variability isv plays a vital role in the initiation and development of el nino events mooring observations reveal contrasting characteristics of upper ocean zonal current isv during different el nino events compared to the 1997 1998 event isv of the 2015 2016 event was significantly weaker by around 30 50 over the equatorial pacific basin and the variability maximum was shifted to the east similar to 160 degrees e these differences can be largely explained by wind forcing features isv of surface winds in 2015 is overall weaker than in 1997 intraseasonal westerly wind bursts in 1997 occurred near the western boundary and originated from the indian ocean whereas in 2015 perturbations were mainly propagated from the northeast pacific and achieved the peak power at similar to 160 degrees e of the equator these changes are likely associated with the decadal warming of the northeast subtropical pacific and weakening of the indian ocean intraseasonal oscillation plain language summary sea surface warmings of strong el nino events are usually triggered by intraseasonal oscillations prior to the events particularly intraseasonal eastward ocean currents generated by westerly wind bursts carry the warm water of the western pacific warm pool to the central pacific and contribute to the surface warming in this paper we compare the intraseasonal zonal current variations during two strong el nino events namely the 1997 1998 and 2015 2016 events although the two el nino events were of comparable strengths intraseasonal variations in 1997 were stronger than those in 2015 by 3050 these differences can be largely explained by the contrasting features of wind forcing intraseasonal oscillations were originated from the indian ocean in 1997 whereas those in 2015 were mainly from the northeast subtropical pacific the varying origin is likely associated with the warming of the northeast subtropical pacific and weakened indian ocean intraseasonal oscillation during recent years

the role of melt in the uplift and exhumation of orogenic belts abstract in some orogenic belts rapid pulses of uplift occur when melt is present detailed work on the relation of melt to structural and metamorphic features in several localities shows that hot metamorphic rocks and especially anatectic migmatite can be physically transported from the lower to middle crust on decollements the decollements form in the lower crust because even though the lower crust is structurally weak throughout due to thermally activated crystal plastic deformation mechanisms the crust is substantially weakened where melt forms or is intruded melt in the lower crust is present long enough to accomodate strain whereas in the upper crust it crystallizes too fast to be a factor in strain localization following crustal loading due to thrusting exhumation results in the formation of additional melt in the migmatites due to decompression melting support of this sequence of events includes 1 evidence for near isothermal decompression of high temperature metamorphic rocks with early high pressure minerals having formed pre or synchronous with penetrative deformation and with lower pressure minerals having formed after the deformation 2 the occurrence of magma sheets that occur along decollements between high temperature metamorphic rocks and lower temperature metamorphic rocks in either thrust or normal configurations 3 nearly concordant k ar cooling dates for biotite and hornblende suggesting rapid cooling rates and 4 post tectonic intrusions of leucogranite or leucotonalite that may represent the products of decompression melting the crystalline slabs of the high himalaya the compressional surges of the coast orogen of british columbia and alaska the cordillera of southern british columbia and the southern belt of the hercynian chain are examples where melt assisted rapid pulses of uplift appear to have occurred during the terminal phases of uplift and following uplift these orogenic belts were exhumed during extension while melt was still present

role of non linear oceanic processes in the response to westerly wind events new implications for the 1997 el nino onset in march 1997 a strong westerly wind event wwe occurred in the western equatorial pacific prior to the 1997 1998 el nino event it produced downwelling kelvin waves that interacted non linearly with the surface temperature salinity and zonal current fronts located at the eastern edge of the warm fresh pool eewp this non linear interaction locally increased zonal currents by a factor of three compared to a theoretical linear response and advected the eewp at an unexpected rate 1m s to which the ocean atmosphere coupled system may have been responding rapidly to trigger el nino conditions