the role of the tropical west pacific in the extreme northern hemisphere winter of 2013 2014 in the 2013 14 winter the eastern usa was exceptionally cold the bering strait region was exceptionally warm california was in the midst of drought and the uk suffered severe flooding it has been suggested that elevated ssts in the tropical west pacific twpac were partly to blame due to their producing a rossby wavetrain that propagated into the extratropics we find that seasonal forecasts with the tropical atmosphere relaxed towards a reanalysis give 2013 14 winter mean anomalies with strong similarities to those observed in the northern hemisphere indicating that low latitude anomalies had a role in the development of the extremes relaxing just the twpac produces a strong wavetrain over the north pacific and north america in january but not in the winter mean this suggests that anomalies in this region alone had a large influence but cannot explain the extremes through the whole winter we also examine the response to applying the observed twpac sst anomalies in two atmospheric general circulation models we find that this does produce winter mean anomalies in the north pacific and north america resembling those observed but that the tropical forcing of rossby waves due to the applied sst anomalies appears stronger than that in reanalysis except in january therefore both experiments indicate that the twpac influence was important but the true strength of the twpac influence is uncertain none of the experiments indicate a strong systematic impact of the twpac anomalies on europe

chronology and mechanism of depletion in lewisian granulites the pattern of th u and rb depletion has been investigated in a suite of contrasting lithologies from the classic lewisian granulite terrain at scourie n w scotland the study is based on lithologies ranging from ultramafic to tonalitic gneisses together with calcsilicate and pelitic metasediments sampled on the metre scale because of their close proximity all of these lithologies have experienced identical p t t histories since depletion however their expected dehydration and melting characteristics are markedly different pb isotope analyses of the samples define the latest time of u pb fractionation as 2 665 0 026 ga and indicate substantial u and th depletion relative to pb in tonalitic and mafic lithologies and in some metasediments in contrast ultramafic samples show no u and th depletion sm nd isotope analyses of the mafic and ultramafic samples define an age of 2 707 0 052 ga which is interpreted as the time of igneous differentiation of the mafic ultramafic bodies this time is indistinguishable from the latest time of th pb and u pb fractionation overall there is a straightforward relationship between the magnitude of depletion lithology and the stability of mineral phases tonalitic and mafic gneisses are depleted in th and u relative to pb whereas ultramafic gneisses which retain amphibole show no evidence for depletion the observations are consistent with loss of u th and rb in fluids produced by metamorphic dehydration and melting a role for externally derived co2 in the depletion process is not excluded by the data but there is no evidence for it having existed limits are placed on the length scale of transport for several elements u th and rb are depleted regionally from mafic and tonalitic lithologies transport distances must have been on the kilometre scale in contrast movements of sm and nd have been more restricted

pb isotopic evidence for u th pb behaviour in a prograde amphibolite to granulite fades transition from the lewisian complex of north west scotland implications for pb pb dating abstract two end member types of u pb fractionation behaviour are recognised type i in which pb isotopic homogenisation occurs and type ii in which pb isotopic homogenisation is incomplete or absent type ii can be further subdivided into three categories depending upon the relationship of the post fractionation 3 238 u 204 pb value to prefractionation 2 in type iia 3 is unrelated to 2 in type iib 3 k 2 where k is a constant in type iic 3 values are uniform each of these types of behaviour results in a predictable effect upon observed uranogenic pb isotope systematics which may lead to an incorrect geochronological interpretation an example of the relationship between these specific types of u pb behaviour and metamorphic grade is provided from the late archaean lewisian complex of n w scotland this complex was metamorphosed during the 2660 ma badcallian event three suites of tonalitic granodioritic grey gneisses have been analysed pyroxene granulite facies from scourie hornblende granulite facies from gruinard bay and amphibolite facies from the northern region the present day pb isotopic composition of these suites can be interpreted as representing a transition from type lib behaviour in the lowest grade rocks resulting in a rotated isochron through type ha in the hornblende granulites which yield a scatter of data points to type i in the pyroxene granulites which yield an isochron corresponding to the badcallian event this transition presumably reflects increasing u depletion with metamorphic grade and ultimately at the highest grade pb mobility and or depletion in addition a consideration of the thorogenic pb isotopic data reveals a systematic variation during prograde metamorphism an attempt to test the model of 2660 ma initial ratio inhomogeneity by analysis of k feldspars from the amphibolite facies gneiss suite reveals 1700 ma laxfordian resetting of their pb isotope systematics this study has implications for pb pb geochronological data particularly in lower grade metamorphic terrains it suggests that reliable isochrons may only be generated by type i behaviour or by the imposition of high 3 values during type iia behaviour at higher grades of metamorphism

sm nd evidence for diachronous crustal accretion in the lewisian complex of northwest scotland sm nd whole rock analyses of several cogenetic rock suites from the late archaean lewisian complex of northwest scotland yield chronological data for a crustal accretion differentiation superevent cads in this terrane three layered mafic ultramafic bodies predate badcallian high grade metamorphism 2660 ma but their temporal relationship to the igneous precursors of the host quartzofeldspathic gneiss complex remains unclear regression of data from these samples yield the following achiltibuie 2850 95 ma with nd t 1 93 0 52 drumbeg 2910 55 ma with nd t 1 70 0 32 scouriemore 2670 110 ma with nd t 0 98 0 73 these data suggest that contemporaneous sub lewisian mantle had a long term light rare earth element depleted history relative to a chondritic reservoir composition three suites of quartzofeldspathic gneisses the pyroxene granulites of scourie the hornblende granulites of gruinard bay and the amphibolites of the northern region north of loch laxford have small ranges of sm nd ratios and do not yield precise regression results if these gneisses were derived from a relatively homogeneous source region perhaps represented by the mafic ultramafic bodies then sm nd model ages suggest a diachronous sequence of crustal generation decreasing in age from scourie terrane average tdm 2930 ma through gruinard bay 2860 ma to the northern region 2780 ma a diachronous sequence such as this suggests that for a cads in which separate accretion and differentiation episodes may be resolved final high grade metamorphism may not be related to magmatic crustal generation processes

the mesoproterozoic supercontinent atlantica in the brazilian shield review of geological and u pb zircon and sm nd isotopic evidence abstract supercontinent atlantica was formed in south america by the orogenies of the trans amazonian cycle namely the accretionary encantadas orogeny 2250 2100 ma and the collisional camboriu orogeny 2100 2000 ma large belts 500 to more than1000 km long formed during the trans amazonian cycle in the three major cratons of south america in the northern part of the amazon craton in the sao francisco craton and in the rio de la plata craton however other large 1000 km segments of archean crust remained little deformed in the cratonic interior of supercontinent atlantica such as a major portion of the tocantins province in central brazil in addition smaller fragments up to 100 km of trans amazonian cycle continental crust are present inside the neoproterozoic brasiliano cycle orogenic belts in the eastern half of extra andean south america in contrast the dominant volume about 90 of neoproterozoic belts was formed by reworking of archean and paleoproterozoic crust zircon u pb geochronology associated with nd isotopes indicates the widespread presence of supercontinent atlantica crust in south america and sensitive high mass resolution ion microprobe investigation of zircons indicates that crust in southern brazil was formed mostly in the trans amazonian cycle zircon geochronology also reveals that supercontinent atlantica was preceded by an intra cratonic period lasting about 300 my and was succeeded by an intra cratonic period of about 1000 to 1300 my many of the trans amazonian cycle belts and crustal fragments may have been accreted to south america during the neoproterozoic the demonstration that they all were once part of supercontinent atlantica must await further multi technique investigations

understanding and modelling extra tropical teleconnections with the indo pacific region during the northern winter teleconnections originated by anomalous heat sources over the tropical indo pacific oceans are investigated in this paper comparing observational results with numerical simulations run as part of the re forecast set for the latest ecmwf seasonal forecasting system system 4 we show that the traditional methodology of linearly relating circulation anomalies to sst anomalies while appropriate for signals originated in central and east pacific fails to adequately identify the response to anomalous heating over the west pacific and most of the indian ocean because of the relatively weak or even negative correlation between sst and rainfall anomalies in these regions instead if teleconnections are computed from covariances with rainfall anomalies a stronger consistency is found between observed and modelled patterns as well as between diagnostics derived from seasonal and intra seasonal time scales the main mode of inter annual variability in indo pacific rainfall associated with planetary scale teleconnections is a tri polar structure with two positively correlated centres in the western indian ocean and the central pacific and a third centre around the maritime continents which is anti correlated with the other two in the extratropical response positive rainfall anomalies over the western and central indian ocean wcio are connected with a negative height anomaly centred over alaska and a positive north atlantic oscillation nao signal in a way reminiscent of the cold ocean warm land pattern this teleconnection cannot be explained by the enso forced component of indian ocean rainfall and is in phase with signals associated with the madden julian oscillation results from the system 4 re forecasts show that the ecmwf coupled model reproduces the broad features of tropical and extratropical teleconnections with a good degree of fidelity however the model significantly over estimates the correlation between rainfall anomalies in the wcio with those over the western and central pacific the impact of this deficiency on the extratropical flow is to weaken the relationship between the nao and indian ocean rainfall on the seasonal scale and to affect the projection of the enso response on the nao finally we argue that reproducing the correct relationship between sst and rainfall anomalies in different part of the indo pacific basin is also crucial for the correct simulation of inter decadal variability particular care should be taken in interpreting results of agcm simulations with prescribed sst where the absence of feedbacks between convection and sst over the warm pool region affects the simulation of rainfall anomalies

north atlantic weather regimes response to indian western pacific ocean warming a multi model study 1 the extratropical large scale atmospheric circulation is often described in terms of a few preferred and recurrent patterns referred to as weather regimes here we investigate the influence of the observed indian and western pacific ocean ip warming over the last decades on the frequency of occurrence of north atlantic weather regimes a multi model approach is adopted in which five different atmospheric general circulation models are forced with idealized sea surface temperature patterns mimicking the ip warming despite some discrepancies three models suggest a stronger occurrence of the zonal regime when ip is warm compensated by less frequent greenland anticyclone regimes consistently with the observed positive trend of the north atlantic oscillation the other two models simulate instead an increase in the frequency of occurrence of the atlantic ridge regime variance decomposition into stationary and transient waves suggest two mechanisms at work in the individual models the ar regime favoured occurrence is associated with a strong transient wave activity along the wave guide in the north pacific and downstream in the north atlantic the zonal favoured excitation is interpreted as an indirect response to changes in the tropical atlantic associated with a global alteration of the walker cell

structural evolution and tectonic setting of the porongos belt southern brazil the sw ne striking porongos belt located between juvenile neoproterozoic rocks in the west and the dom feliciano belt characterized by intense reworking of older crust in the east comprises a greenschist to amphibolite facies metavolcano metasedimentary succession porongos sequence of unknown age with some exposures of palaeoproterozoic gneisses encantadas gneisses high temperature ductile deformation of the basement gneisses comprises at least two magmatic events followed by three deformational phases including folding and shearing dt1 dt3 and can be attributed to the palaeoproterozoic trans amazonian orogeny the deformation of the porongos sequence occurred during the neoproterozoic brasiliano orogeny and comprises four ductile deformation phases db1 db4 including two phases of isoclinal folding associated with shearing recorded in mylonitic layers followed by closed nw vergent folding and thrusting leading to formation of a thrust stack uplift of the basement and formation of late tectonic sedimentary basins occurred as a result of semi ductile to brittle block faulting in a sinistral strike slip regime the porongos sequence can be subdivided into a southeastern and a northwestern part trace element analyses as well as sm nd and rb sr geochemical data indicate partial melting and significant contamination by old continental crust for the metavolcanic rocks the metavolcanic rocks show end t 780 ma values of 20 64 and 21 72 northwestern units and 6 87 southeastern sequence the metasedimentary rocks were derived from late palaeoproterozoic to archaean sources and the data indicate different sources for the northwestern and southeastern rock units of the porongos sequence end t 780 ma are 6 25 and 6 85 in the southeastern units with tdm model ages between 1734 and 1954 ma and vary between 14 72 and 17 96 in the northwestern parts which have tdm model ages between 2346 and 2710 ma high 87 sr 86 sr t values between 0 7064 and 0 7286 confirm reworking of older crust isotopic signatures of the porongos sequence do not show indications for a significant contribution from a neoproterozoic juvenile source a passive margin or continental rift environment is suggested for the tectonic setting of the porongos belt which is compatible with both deposition of shallow marine to deep marine sediments and stretching of continental crust leading to volcanism which is characterized by significant contamination by old continental crust

fracture sealing in zircon as evaluated by electron microprobe analyses and back scattered electron imaging abstract the internal structure of zircon is commonly revealed by back scattered electron bse images grains from a 750 700 ma old talc alkaline mafic metatonalite from southernmost brazil show relict igneous faces irregular and diffuse metamorphic overgrowths and fracture sealing sealing of fractures is observed as light grey patches in bse images epma profiles show strong but differential increases in hf and u in the sealed fractures unlike the common assertion in the literature that fractures are only pathways of leaching sealing of fractures occurs near borders of grains as well as in their cores and is not visible during standard petrographic examination thus careful bse image evaluation is needed before either in situ or whole grain isotopic determinations are made

sm nd dating and cooling history of scourian granulites sutherland the scourian gneisses of the lewisian complex of north west scotland have been the subject of many geochronological investigations sm nd whole rock measurements suggest that the protoliths of the lewisian complex differentiated 2 92 0 05 gyr ago from an approximately chrondritic mantle1 rb sr and pb pb whole rock ages between 2 8 and 2 6 gyr reflect subsequent depletion in rb and u refs 2 3 which has generally been associated with granulite facies metamorphism zircons which are thought to have crystallized during this metamorphism have also given u pb ages of 2 66 gyr ref 4 this granulite facies metamorphism involving pressures in excess of 10 kbar and peak temperatures estimated between 820 50 c ref 5 and 1 250 c refs 6 7 affects a terrain including supracrustal rocks7 and thus implies a major tectonic event we report here the first geochronological data measured on mineral assemblages that have also provided estimates of the conditions of metamorphism such measurements are possible because the major minerals of granulite facies assemblages show an unusually favourable spread in sm nd ratios garnet especially is strongly enriched in sm ref 8 data for three garnetiferous basic gneiss assemblages suggest that closure of the sm nd system occurred significantly later than the peak of the metamorphism

decadal interactions between the western tropical pacific and the north atlantic oscillation the relationship between interdecadal variations of tropical sea surface temperature sst in the last 120 years and circulation anomalies related to the north atlantic oscillation nao is investigated in this study using an atmospheric general circulation model agcm we confirm observational evidence that variations in the sst gradient in the western tropical pacific are related to the nao anomalies on decadal timescale and may be contributing to the shift towards the positive nao phase observed in the late 20th century the role played by the indian ocean nao teleconnection advocated in recent studies focused on the last 50 years is also assessed in the context of the 120 year long record it is suggested that a positive feedback between the pacific sst and the hemispheric circulation pattern embedding the decadal nao signal may act to enhance the internal variability of the coupled ocean atmosphere system and justify the stronger teleconnection found in observational data than in sst forced agcm experiments

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

geochemistry and crustal evolution of volcano sedimentary successions and orthogneisses in the sao gabriel block southernmost brazil relics of neoproterozoic magmatic arcs abstract precambrian metaplutonic rocks of the sao gabriel block in southernmost brazil comprise juvenile neoproterozoic calc alkaline gneisses cambai complex the connection with associated ultra mafic metavolcanic and metasedimentary rocks palma group is not well established the whole complex was deformed during the brasiliano orogenic cycle both metasedimentary and metavolcanic rocks as well as metaplutonic rocks of the cambai complex have been sampled for geochemical analyses in order to get constraints on the tectonic setting of these rocks and to establish a tectonic model for the sao gabriel block and its role during the assembly of west gondwana the major element compositions of the igneous rocks palma group and cambai complex indicate a subalkaline character most orthogneisses have a calc alkaline chemistry many metavolcanic rocks of the palma group show signatures of low k tholeiitic volcanic arc basalts trace element data especially ti zr y nb of most igneous samples from both the lower palma group and the cambai complex indicate origin at plate margins i e in a subduction zone environment this is corroborated by relative enrichment in lree low contents of nb and other high field strength elements and enrichment in lile like rb ba and th the data indicate the possible existence of two suites an oceanic island arc and a continental arc or active continental margin however some ultramafic samples of the lower palma group in the western sao gabriel block indicate the existence of another volcanic suite with intra plate character which possibly represents relics of oceanic island basalts oib trace element data indicate contributions from andesitic to mixed felsic and basic arc sources for the metasedimentary rocks the patterns of chondrite and n morb normalized spider diagrams resemble the patterns of the igneous rocks i e lile and lree enrichment and hfs depletion the geochemical signatures of most igneous and metasedimentary samples and their low 87sr 86sr t ratios suggest only minor contribution of old continental crust a geotectonic model for the sao gabriel block comprises east ward subduction and following accretion of an intra oceanic island arc to the eastern border of the rio de la plata craton at ca 880 ma and westward subduction beneath the newly formed active continental margin between ca 750 and 700 ma the sao gabriel block represents relics of an early brasiliano oceanic basin between the rio de la plata and kalahari cratons this ocean to the east of the rio de la plata craton might be traced to the north and could possibly be linked with neoproterozoic juvenile oceanic crust in the western brasilia belt goias magmatic arc

global atmospheric sensitivity to tropical sst anomalies throughout the indo pacific basin abstract the sensitivity of the global atmospheric response to sea surface temperature sst anomalies throughout the tropical indian and pacific ocean basins is investigated using the ncep mrf9 general circulation model gcm model responses in january are first determined for a uniform array of 42 localized sst anomaly patches over the domain results from the individual forcing experiments are then linearly combined using a statistically based smoothing procedure to produce sensitivity maps for many target quantities of interest including the geopotential height response over the pacific north american pna region and regional precipitation responses over north america south america africa australia and indonesia perhaps the most striking result from this analysis is that many important targets for seasonal forecasting including the pna response are most sensitive to sst anomalies in the nino 4 region 5 n 5 s 150 w 160 e of the central tropical pacific with lesser and sometimes opposite s

amphibolite dehydration melting sorting out the solidus amphibolite melts under vapour absent conditions by dehydration melting during which h 2o released from hornblende is transferred directly into h 2o undersaturated silicate liquid five independent 1991 studies on amphibolite dehydration melting differ from each other and from earlier conceptual treatments five solidi between 7 and 10 kb vary from 975 c to 740 c two solidi above 10 kb are near vertical near 975 c and 850 c some differences are due to different amphibolite compositions and mineralogy we use the results of earlier experiments involving garnet supported by our own new results to construct a closed system phase diagram for a simple fully hydra ted amphibolite hornblende plagioclase showing the solidus and the melting interval for hornblende garnet other minerals liquid the amphibolite vapour absent solidus is defined by the beginnings of two multivariant reactions 1 a near vertical curve large positive d p dt where the formation of augite dominates and 2 a near horizontal curve a t higher pressures where the formation of garnet dominates the solidus curve bends back estimated near 900 c 9 kb with slope changing to low positive dp dt the new phase diagram expands the field for liquid generation with garnet amphibolite residues to much lower temperatures and pressures than the other recent experimental results increasing the range from which small amounts of hydrous granitoid melts may be segregated by compaction the reversed near horizontal slope of the solidus near 10 kb has interesting petrological consequences

granulite fades nd isotopic homogenization in the lewisian complex of northwest scotland a published sm nd whole rock isochron of 2 920 50 myr obtained from a wide range of lithologies in the lewisian complex of north west scotland was interpreted1 as the time of protolith formation this date is 260 myr older than estimates for the timing of high grade metamorphism in the complex at 2 660 myr2 3 and this period is considered to represent the duration of the lewisian crustal accretion differentiation superevent cads 4 here we give new sm nd data obtained specifically from granulite facies tonalitic gneisses that yield a date of 2 600 155 myr although depleted mantle model ages tdm suggest 200 myr of premetamorphic crustal residence the regression date and its associated initial nd isotopic parameters demonstrate nd isotopic homogenization during the high grade event as well as the probability of general rare earth element ree mobility models for selective element depletion in the complex have previously assumed ree immobility since 2 920 myr but the data presented here suggest that a reappraisal of the depletion mechanism is required

genesis of the kapuskasing ontario migmatitic mafic granulites by dehydration melting of amphibolite the importance of quartz to reaction progress migmatitic granulite grade mafic gneisses make up a significant part of the kapuskasing structural zone ksz ontario although they contain a common mineral assemblage hornblende hbl plagioclase pl diopside di garnet grt quartz qtz titanite ttn the mafic gneisses show wide variations in modal mineralogy from hornblende rich to diopside garnet rich varieties and all gradations between up to 25 vol segregated plagioclase quartz rich trondhjemitic leucosome tdh is intimately associated with the mafic gneiss occurring in a continuum of patches veins and transecting dykes at scales ranging from decimetres to micrometres the texture and composition of the leucosome combined with p t estimates for the host rocks above the solidus suggest it represents crystallized trondhjemitic melt quartz is mainly restricted to the segregated leucosomes but more rarely occurs in a variety of interstitial textures in the mafic gneiss suggesting that it crystallized from a melt phase rather than having been present as a solid phase at peak metamorphic conditions modal and textural data indicate a reaction relationship of the form hbl pl qtz grt di ttn leucosome tdh implying that the granulite forming process involved dehydration melting of an amphibolite protolith pressure temperature estimates from grt di pl qtz geothermobarometry are 9 kbar and 685 735 c however based on experimental studies of dehydration melting of amphibolite we estimate that peak conditions were closer to 11 kbar 850 c mass balance analysis using the technique of singular value decomposition and reaction space analysis were used to quantify the reaction and to determine the controls on reaction progress the following mass balance provides a model for the natural reaction 1 00 hbl 0 92 pl 3 76 qtz 1 14 grt 1 54 di 0 21 ttn 1 49 tdh 0 14 pg 0 39 fe 1mg 0 33 nasica 1al 1where pg is a pargasite like exchange in all model mass balances tested quartz is a reactant with a large coefficient we argue that the abundance of quartz in the amphibolite protolith was the primary control on the differing extents of reaction observed mineral compositional variation exerted a secondary control on reaction progress with fe richer layers containing an richer plagioclase and more actinolitic amphibole reacting earliest i e at lowest temperatures comparison of the calculated amount of melt produced in the gneisses with that now observed implies expulsion of 5 30 of the melt these volumes are similar to those predicted from ree modelling of archaean tonalities and trondhjemites from a garnet amphibolite source suggesting that the ksz mafic gneisses may be representative of partially depleted source rocks for trondhjemite tonalite generation

geochemistry and petrology of the jequie granulitic complex brazil an archean basement complex the jequie granulitic complex is part of the extensive high grade metamorphic terrain located within the sao francisco craton of northeastern brazil some jequie rocks appear to have been formed in the middle archean 3 1 ga from preexisting sialic crust the dominant mineral composition of these rocks is quartz microcline plagioclase hyperstene and occurs over an extensive area 2 000 km2

pb pb systematics of lewisian gneisses implications for crustal differentiation combined use of rb sr u pb and sm nd decay schemes in geochronology provides insights into the evolution of ancient continental crust1 such as the lewisian of north west scotland we report here a pb pb whole rock isochron date of 2 950 70 myr on amphibolite facies grey gneisses from the northern region of the lewisian this is essentially the same as a sm nd whole rock isochron date 2 920 50 myr which was interpreted as the time of separation of igneous protoliths from the mantle2 a period of 240 myr separates this date from the scourian peak of granulite facies metamorphism this result indicates for the lewisian that high grade metamorphism and crustal stabilization cannot have been the result solely of thermal equilibration more generally it suggests that tectonic thickening was an important process during archaean crustal evolution3 and that although whole rock systems may remain open with respect to u pb until the termination of granulite facies metamorphism they may be closed during amphibolite facies metamorphism

sm nd isotopic investigation of neoproterozoic and cretaceous igneous rocks from southern brazil a study of magmatic processes abstract nd evolutionary paths for diversified igneous suites from southern brazil are here re evaluated using published results we interpret the end paths considering the secondary fractionation of 147sm 144nd due to major petrogenetic processes the inclusion of nd isotopes and geochemical data for precambrian and mesozoic basic rocks allow improving the discussion on the subcontinental lithosphere beneath southern brazil late neoproterozoic rocks mostly granitoids are exposed in two regions of the southern brazilian shield an eastern collisional belt and a western foreland the latter included two geotectonic domains amalgamated at this time the sao gabriel arc 900 700 ma and the taquarembo cratonic block magma genesis mainly involved mixture of crustal and incompatible element enriched mantle components both with a long residence time continental segments are the neoarchaean paleoproterozoic lower crust ca 2 55 ga in the western foreland and paleoproterozoic neoproterozoic recycled crust 2 1 0 8 ga in the collisional belt granitoids with a single crustal derivation are limited in the southern brazilian shield mixing processes are well registered in the western foreland where the re enriched old mantle was probably mixed with a 900 700 ma old subducted lithosphere and a 2 55 ga old lower crust the contribution of the latter increased from the early 605 580 ma to the later 575 550 ma neoproterozoic events which may be due either to crustal thickening or to delamination of the lithosphere magma sources were diversified in the 660 630 ma collisional belt initially they involved the mixing between two components with similar nd isotopic ratios a 2 1 0 8 ga old recycled crust and a subduction processed old mantle regional heating and abundant production of granitic melts with diversified contribution of enriched mantle components mark the end of the collisional period at 630 580 ma we can also attribute this to the delamination of the lithosphere so that the same geodynamic process may explain the magmatism in the whole shield at the end of the dom feliciano orogeny mesozoic rocks include flood basalts from the cretaceous parana province and sub coeval alkalic suites multiple processes of metasomatism affected the lithospheric mantle resulting in some complexity but they mainly register two enriched mantle components both generated during neoarchaean paleoproterozoic events one end member has a more pronounced subduction signature the other one probably resulted from the re enrichment of the first component at the end of the camboriu collisional orogeny 2 0 ga

sequence stratigraphy of coastal alluvial plain westphalian b coal measures in northumberland and the southern north sea abstract westphalian b coastal alluvial plain coal measures of northumberland and the southern north sea are susceptible to stratigraphic base level fluctuations of various magnitudes which create a hierarchy of flooding surfaces 1 high magnitude third order maximum flooding surfaces corresponding to the anthracoceratites vanderbeckei and anthracoceras aegiranum marine bands defining the top and bottom of the succession when vast areas of the westphalian foreland basin were flooded by marine incursions 2 high frequency fluctuations promoting small scale fourth order flooding of the entire or large areas 100 s km 2 of the alluvial plain resulting in deposition of non marine bivalve beds or marine bands depending on their position on the third order base level curve and 3 small scale localised base level rises due to differential compaction and autocyclic switching of minor crevasse splays and distributary channels a regionally extensive third order tectonically induced sequence boundary is also recognised in the southern north sea slightly above the maximum stand in stratigraphic base level recorded by the vanderbeckei marine band this sequence boundary which represents the lowest point on the background eustatic base level curve between the two maximum flooding surfaces is overlain by the multilateral multistorey caister sandstone the lack of significant erosional relief beneath this channel sandstone suggests that accommodation space at this time was being created at a very low rate the succession above the caister sandstone sequence boundary up to the aegiranum marine band maximum flooding surface records an increasing rate of stratigraphic base level rise this equates to a third order transgressive systems tract or sequence set comprising a number of fourth order sequences which change upwards in response to the background low frequency rise the increasing rate of base level rise and increased accommodation space is accompanied by a change in fluvial style to more isolated channels enclosed within floodplain deposits

zoning patterns in orthopyroxene and garnet in granulites implications for geothermometry compositional maps of orthopyroxene and garnet of contrasting grain size and in contact with different minerals were made from two paragneiss granulites from the minto terrane of northern quebec the compositional maps provide clear evidence of late exchange of fe fe mg after ca in garnet and al in orthopyroxene had been quenched in the extent of late fe mg exchange was controlled by neighbouring minerals with negligible fe mg gradients against plagioclase and quartz and substantial gradients against exchangeable fe mg minerals cores of grains in contact with exchangeable fe mg neighbours are progressively more reset in fe fe mg as grain size decreases whereas cores of even small grains surrounded by only plagioclase and quartz are not significantly different in fe fe mg than cores of the largest grains gradients of ca in garnet and of al in orthopyroxene in grains of uniform fe fe mg preserve a high temperature retrograde history during which intergranular exchange effected compositional uniformity of mineral rims and intragranular fe mg diffusion in garnet and orthopyroxene was rapid enough to homogenize fe fe mg the transition from efficient intergranular exchange at relatively high temperatures to local fe mg exchange at lower temperatures may have been controlled by loss of an intergranular exchange medium in the rock possibly an internally generated dehydration melt phase implications for geothermometry of granulites include the following numerical values are particular to this study 1 core compositions of garnet and orthopyroxene grains in contact with exchangeable neighbours may be reset in fe fe mg relative to the most refractory compositions by an amount equivalent to 120d c 2 fe mg exchange thermometry using even the most refractory fe fe mg compositions may not record peak granulite conditions possibly recording instead the temperature at which an intergranular exchange medium was lost from the rock and 3 temperature sensitive net transfer equilibria involving al solubility in orthopyroxene yield temperatures up to 150d c higher than maximum fe mg exchange temperatures even in grains with flat fe fe mg compositional profiles making them a better means of estimating peak granulite temperatures than fe mg exchange thermometry

partial melting of subducting oceanic crust the conditions under which partial melting of subducting oceanic crust occurs can be determined by combining a partial melting model for basaltic compositions with two dimensional thermal models of subduction zones for porosities of 1 containing h20 the amount of partial melt generated at the wet basaltic solidus is limited to 100 mpa can be maintained by rocks close to or above their melting temperatures in the absence of high shear stresses substantial melting of the oceanic crust will only occur during subduction of very young 5 ma oceanic lithosphere partial melting of hydrated basalt amphibolites derived from the mid ocean ridge has been proposed e g 1 3 as being responsible for the generation of certain recent high al andesitic to dacitic volcanic rocks adakites three of these volcanic suites mount st helens southern chile and panama occur in volcanic arcs where oceanic crust 25 ma is being subducted at rates of 1 3 cm yr and the calculated thermal regime is several hundreds of degrees hotter than more typical subduction zone environments however oceanic lithosphere is not currently being subducted beneath baja and new guinea where recent adakites are also present suggesting that some adakite magmas may form by water undersaturated partial melting of underplated mafic lower crust or previously subducted oceanic crust further experimental work on compositions representative of oceanic crust is required to define the depth of possible adakite source regions more accurately

archaean crustal development in the lewisian complex of northwest scotland the lewisian complex of northwest scotland is typical of many archaean terrains and has a well documented history starting 2 700 myr ago1 6 here we present new isotopic data that extend this history back to 3 300 myr and provide some insight into how the earliest continental crust may have formed the lewisian is dominated by tonalite trondhjemite and granodiorite ttg rocks which require a mafic lithospheric source rather than being direct mantle melts7 11 but the mafic and ultramafic rocks in the high grade granulite facies part of this terrain show little evidence of a significantly older crustal history12 13 and precursor material to the ttg lithologies has not yet been identified here we show that older amphibolite material has survived at a lower metamorphic grade coexisting amphibolite minerals yield indistinguishable 207pb 206pb and 147sm 143nd ages of 3 310 27 myr and 3 298 73 myr respectively these data are consistent with an origin for much of the lewisian terrain by the re melting of preexisting lithosphere with an isotopic signature similar to that of the amphibolites studied here

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

deepest exposed crust of brazil geochemistry of paleoproterozoic depleted santa maria chico granulites abstract the deepest crustal processes of brazil are investigated in the santa maria chico granulitic complex of rio grande do sul state depth of ca 30 km is inferred from garnet bearing mafic granulite geobarometry for the deformation of the bimodal basic acid sequence of late archean age this low k tholeiitic magmatism occurred in an island arc environment which accreted to the atlantica supercontinent in a collisional episode at ca 2 1 ga during the transamazonian cycle although this magmatism is strongly depleted in lithophile elements its geochemistry is still magmatic and shows that the metamorphism did not disturb the original distribution of the elements in the host rocks significantly the associated trondhjemites could have been the differentiated portions of the basic magmas but more likely were the result of the partial melting of the garnet bearing mafic residue this suite of high grade rocks is one of several protoliths for the generation of the abundant k granites of the 600 ma brasiliano cycle from southern brazil this high grade rock association is rather comparable to the lewisian complex of scotland

multiple accretion at the eastern margin of the rio de la plata craton the prolonged brasiliano orogeny in southernmost brazil the neoproterozoic eoplalaeozoic brasiliano orogeny at the eastern margin of the rio de la plata craton in southernmost brazil and uruguay comprises a complex tectonic history over 300 million years the southern brazilian shield consists of a number of tectono stratigraphic units and terranes the sao gabriel block in the west is characterized by c 760 690 ma supracrustal rocks and calc alkaline orthogneisses including relics of older c 880 ma old igneous rocks both igneous and metasedimentary rocks have positive end t values and neoproterozoic tdm model ages they formed in magmatic arc settings with only minor input of older crustal sources a trondhjemite from the sao gabriel block intruding dioritc and tonalitic gneisses during the late stages of deformation d3 yield an u pb zircon age la icp ms of 701 10 ma giving the approximate minimum age of the sao gabriel accretionary event the encantadas block further east containing the supracrustal porongos belt and the pelotas batholith is in contrast characterized by reworking of neoarchean to palaeoproterozoic crust the 789 7 ma zircon age of a metarhyolite intercalated with the metasedimentary succession of the porongos belt provides a time marker for the basin formation zircons of a sample from tonalitic gneisses constituting the palaeoproterozoic basement of the porongos belt form a cluster at 2 234 28 ma interpreted as the tonalite crystallization age zircon rims show ages of 2 100 2 000 ma interpreted as related to a palaeoproterozoic metamorphic event the porongos basin formed on thinned continental crust in an extensional or transtensional regime between c 800 700 ma the absence of input from neoproterozoic juvenile sources into the porongos basin strongly indicates that the encantadas and sao gabriel blocks were separated terranes that became juxtaposed next to each other during the brasiliano accretional events the tectonic evolution comprises two episodes of magmatic arc accretion to the eastern margin of the rio de la plata craton i accretion of an intra oceanic arc at c 880 ma passinho event and ii accretion of the 760 700 ma cambai vila nova magmatic arc sao gabriel event the latter event also includes the collision of the encantadas block with the rio de la plata craton to the west collision and crustal thickening was followed by sinistral shear along sw ne trending orogen parallel crustal scale shear zones that can be traced from southern brazil to uruguay and have been active between 660 and 590 ma voluminous granitic magmatism in the pelotas batholith spatially related to shear zones is interpreted as late to post orogenic magmatism possibly assisted by lithospheric delamination it marks the transition to the post orogenic molasse stage localized deformation by reactivation of preexisting shear zones continued until c 530 ma and can be assigned to final stages of the amalgamation of west gondwana

polymetamorphic evolution of the lewisian complex nw scotland as recorded by u pb isotopic compositions of zircon titanite and rutile u pb isotopic relations in zircon and titanite of granulite and amphibolite gneisses in the lewisian complex and bordering laxford front reveal complex discordance patterns indicating multiple late archean and early proterozoic crystallization overgrowth and pb loss events the earliest stages in the evolution of the complex remain poorly resolved zircon ages of 2710 ma date high grade metamorphism and magmatism probably related to tectonic and magmatic accretion in a continental arc setting a distinct event at 2490 2480 ma possibly initiated by metamorphism and deformation at high grade conditions caused amphibolitization of the granulites and emplacement of granitic pegmatites this event can be correlated with development of inverian shear zones and formation of granitoid layers along the laxford front the emplacement of a younger generation of granitoid sheets during the laxfordian event fromed hydrothermal titanite at 1754 ma in gneisses south of the laxford bridge and partially reset older titanite at scourie growth of secondary titanite and rutile also occurred during subsequent low grade metamorphism at 1690 1670 ma

the application of high resolution sequence stratigraphy to fluvial systems a case study from the upper carboniferous breathitt group eastern kentucky usa the pennsylvanian pikeville hyden and four corners formations of the breathitt group in eastern kentucky usa contain six major facies associations along with a number of subassociations these facies associations are offshore siltstone rhythmically bedded mouthbar heteroliths predominantly fine grained floodplain deposits minor channel fills major distributary channels and major stacked fluvial bodies the stacked fluvial bodies are incised into a variety of open marine and delta plain deposits have widths of several kilometres and exhibit a range of sandy fill types these fluvial complexes are interpreted as incised valley fills parasequences and parasequence sets are not identifiable nonetheless it is possible to identify systems tracts on the basis of sequential position facies associations and systematic changes in architectural style and sediment body geometries the studied portion of the breathitt group comprises stacked 4th order sequences which occur in lowstand transgressive and highstand sequence sets related to the development of a lower frequency base level cycle in the lowstand sequence set incision associated with successive 4th order sequence boundaries has commonly removed all the hst and tst of the underlying sequences such that succeeding 4th order incised valley fills are amalgamated within the transgressive sequence set incision is at a minimum and incised valley fills tend to stack discretely with the maximum amount of fine grained tst and hst between them the highstand sequence set is transitional between the lowstand and transgressive sequence sets in terms of the amount of transgressive and highstand deposits preserved incised valley fills tend to stack discretely

planetary scale variability in the northern winter and the impact of land sea thermal contrast this paper investigates the impact of land sea thermal contrast on large scale modes of variability during the northern hemisphere winter with specific attention to those modes which explain a large proportion of the observed inter decadal changes in the late 20th century two possible mechanisms are considered where the land sea contrast plays either a passive or an active role namely the introduction of zonal asymmetries in an eddy driven annular mode and variations in the thermal balance of a planetary wave pattern with zonal wavenumber 2 in addition to diagnostics based on re analysis data two long perpetual winter simulations of an intermediate complexity agcm are performed imposing surface boundary conditions with either realistic or artificially reduced land sea thermal contrast on the basis of previous studies indices derived from surface fields are defined to represent the two mechanisms outlined above atmospheric patterns co varying with these indices are first computed from ncep ncar re analysis and compared with traditional definitions of dominant modes of variability such as eofs and the cold ocean warm land cowl pattern subsequently the indices are applied to fields from the simulations with realistic and reduced land sea contrast in order to highlight the impact of thermal asymmetries on the structure of annular and planetary wave modes our results show that the zonal thermal contrast on the western border of the north atlantic is responsible for the localization of a dipolar structure in sea level pressure and height fields which bears a strong resemblance to the north atlantic oscillation nao in this region the response to thermal land sea contrast is evident on both annular and planetary wave patterns with a nao like dipole being the dominant regional feature in the north pacific on the other hand diabatic forcing is balanced primarily by meridional temperature advection because here contrarily to the north west atlantic region the surface temperature gradient is stronger in the meridional than in the zonal direction therefore the modification of the annular mode by zonal temperature advection at the asia north pacific border produces a different pattern from that associated with the thermal balance of a cowl like planetary wave we conclude that thermally balanced wave mode is a dynamically appropriate description for the pattern previously identified as the second eof of low frequency 500 hpa height variability or empirically defined as the cold ocean warm land pattern since this mode accounts for a large proportion of the upper air inter decadal variations in the second half of the 20th century we suggest that such variations are dynamically consistent over the hemispheric domain therefore they should be understood in terms of planetary scale dynamics rather than by the casual superposition of regional effects

the mechanisms of petrogenesis of the archaean continental crust comparison with modern processes the petrographic and chemical composition of magmatic rocks generated during the archaean appears to be different from that of post archaean rocks komatiites are widespread before 2 5 ga and rarely occur afterwards in addition the archaean continental crust is primarily ttg tonalitic trondhjemitic and granodioritic in composition exhibiting typical trondhjemitic differentiation trends whereas modern equivalents are granodioritic to granitic following classical calc alkaline differentiation trends this distinction becomes more prominent when rare earth elements ree are taken into account archaean ttg are yb poor ybn 8 5 and have high layb ratios 5 layb n 150 in comparison the post 2 5 ga granitoids emplaced in subduction zone geodynamic environments have high yb content 4 5 ybn 20 with very low layb n ratios 20 theoretical calculations and experimental petrology have shown that the ttg can be produced by partial melting of an archaean tholeiite transformed into garnet bearing amphibolite consequently the low heavy ree content of the ttg is explained by the influence of both residual garnet and hornblende in their source after 2 5 ga the role of these minerals in calc alkaline magma genesis becomes progressively less important which is interpreted in terms of a cooling earth model in modern subduction zone environments the subducted oceanic slab is relatively old and cold and the geothermal gradient along the benioff plane in low ca 10 c km consequently the down going lithosphere undergoes dehydration before partial melting is able to occur the liberated fluids are light ree and lile enriched and ascend into the overlying mantle wedge where they induced partial fusion the produced magmas separate from their mantle source region leaving a residue mainly composed of olivine and pyroxenes mantle derived magmas typically exhibit high yb contents due to low kdyb values for olivine and pyroxenes during the archaean the subducted lithosphere was relatively young and hot providing high geothermal gradients along the benioff zone thus partial melting of the subducted slab was possible at lower temperatures before dehydration would take place garnet and hornblende are the main residual phases accounting for the low yb contents of the archaean ttg this model can be tested using a modern analogue of archaean like subduction processes in south chile an oceanic ridge has subducted and all thermodynamic calculations indicate that this creates locally high geothermal gradients along the benioff zone thus in very small areas archaean like environments may be simulated in modern subduction zones the modern andesites produced in this environment show archaean geochemical characteristics with low ybn 5 whereas the majority of andesites along the andean arc have modern patterns with ybn ranging from 8 to more than 17 this conclusion was generalised to all young subducted lithospheres all over the world in conclusion it appears that since the archaean there has been a change in the site of continental crust genesis the location of calc alkaline magma source in subduction zone environments has migrated through time from the subducted slab to the mantle wedge this is a direct consequence of the progressive cooling of the earth

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

sm nd isotope geochemistry of metamorphic volcano sedimentary successions in the sao gabriel block southernmost brazil evidence for the existence of juvenile neoproterozoic oceanic crust to the east of the rio de la plata craton abstract juvenile neoproterozoic dioritic tonalitic trondhjemitic and granodioritic gneisses in the sao gabriel block southern brazil have been identified by geochronologic studies age proposals for associated ultra mafic metavolcanic and metasedimentary rocks however range from archean to neoproterozoic whole rock sm nd analyses presented here support a neoproterozoic age for these rocks tdm model ages of the ultra mafic metavolcanic rocks range between 0 65 and 1 35 ga with nd t positive values between 3 16 and 6 87 tdm model ages of metasedimentary and metavolcanoclastic rocks vary between 0 77 and 1 19 ga with nd t values between 1 2 and 6 23 tonalitic calc alkaline gneisses show nd t values of 4 34 and 6 3 and tdm model ages of 0 89 and 0 72 ga respectively a late kinematic granite santa zelia granite display slightly negative nd t values 1 6 and a higher tdm model age of about 1 4 ga these data support the existence of meso neoproterozoic juvenile oceanic crust and island arc rocks during the brasiliano orogenic events the main source rocks of the metasedimentary units are previously formed juvenile rocks the data also indicate minor assimilation of older crustal material and or contamination of the melts by radiogenic nd released from older rocks on the subducting slab existence of widespread old sialic crust in the subduction zone environment however can be ruled out indicating important orogenic accretion between 0 9 and 0 7 ga a geotectonic model for the sao gabriel block and the eastern margin of the rio de la plata craton comprises eastward subduction and following accretion of an intra oceanic island arc between 0 9 and 0 8 ga and a subsequent westward subduction with formation of an active continental margin at the eastern margin of the rio de la plata craton between 0 8 and 0 7 ga we postulate that the juvenile rocks of sao gabriel block represent relics of a neoproterozoic ocean between the rio de la plata craton and a continental block encantadas block possibly derived from the kalahari craton subduction and arc accretion began roughly coeval with the initial stages of the break up of rodinia 0 9 ga and indicate a peripheric rio de la plata craton in relation to the rodinia supercontinent with evolution from a passive margin to an active margin in the beginning of the neoproterozoic brasiliano orogenic events

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

impact of localized tropical and extratropical sst anomalies in ensembles of seasonal gcm integrations a series of 120 day ensemble integrations of a general circulation model designed to assess the impact of geographically localized sea surface temperature sst anomalies in both the tropics and extratropics are described these experiments contribute firstly to an appraisal of the relative roles of tropical and extratropical sst anomalies on interannual variability of the large scale circulation in the northern extratropics and secondly to an assessment of the role of quasi stationary diabatic heating anomalies on model systematic error including blocking activity overall it is found that sst anomalies associated with el nino and la nina have a larger and more reproducible impact on the extratropics than the chosen extratropical sst anomalies these extratropical anomalies were localized to the north west pacific and north west atlantic with realistic amplitude however unlike earlier studies a response to the extratropical north pacific sst anomalies has been obtained over the north pacific which is correlated with the sign of the imposed sst anomaly the response to extratropical sst anomalies in the north west atlantic are similar to the results obtained from an earlier study the downstream responses to the extratropical pacific and atlantic sst anomalies are qualitatively similar to one another overall it is concluded that the northern large scale flow is influenced by such extratropical sst anomalies the response to idealized tropical sst anomalies was also studied in particular a localized anomaly over indonesia had a very substantial impact on the hadley circulation on zonal flow and on blocking frequency over the north pacific and europe this response was such as to reduce model systematic error locally in the vicinity of the sst anomaly remotely around the tropics and remotely in the extratropics a similar though weaker impact on euro atlantic blocking was obtained with an idealized caribbean sst anomaly further statistical and dynamical analyses suggested that the extratropical response to the indonesian sst anomaly occurs through the creation of two distinct planetary scale regimes in one of which the formation of blocks is much favoured by increased ridges on the north eastern side of the oceans

charnockite geobarometers based on coexisting garnet pyroxene plagioclase quartz numerous geothermometers based on compositions of coexisting minerals have been calibrated experimentally or theoretically during the past 10 yr in contrast few continuous reaction geobarometers exist which have had wide application one based on the reaction of cordierite to garnet sillimanite and quartz is limited by a relatively narrow pressure range of application and also by conflicting calibrations1 2 because the mixing relations of mg and fe and the role of h2o in cordierite3 are not understood another successful barometer uses the assemblage garnet plagioclase al2sio5 and quartz4 5 continuous geobarometers based on the reaction of orthofer rosilite to fayalite plus quartz6 and on the aluminium content of enstatite in equilibrium with garnet7 have been used to a lesser extent the former barometer is limited by rarity of the requisite assemblage and the latter by uncertain experimental calibration for crustal rocks we calibrate here two mineralogical geobarometers from measured thermodynamic data the participating minerals pyroxenes garnet plagioclase and quartz are frequently associated in high grade metamorphic rocks calculation of pressures for several terrains show that the geobarometers yield reasonable and consistent results for the entire range of crustal pressures

volcanic cycles and setting in the neoproterozoic iii to ordovician camaqua basin succession in southern brazil characteristics of post collisional magmatism the camaqua basin comprises a volcano sedimentary succession located in southernmost brazil and represents a molasse basin formed at the post collisional stage of the brasiliano pan african orogenic cycle in the neoproterozoic iii to ordovician period this basin is one of the most well preserved ancient volcano sedimentary sequences undeformed and unmetamorphic in the world dominantly developed on a continental setting under subaerial conditions it is composed of five major stratigraphic units four of them with a distinct volcanic character from the bottom to the top as 1 marica 2 bom jardim 3 acampamento velho 4 santa barbara and 5 guaritas allogroups a concise sight of geochemical and isotopic rock data is presented as well as stratigraphic correlation and description of rock structures and textures that lead to the identification of their genetic processes the aim of this paper indicating a relation with a coeval plutonism and volcanism that evolved from high k calc alkaline to shoshonitic and ended with a silica saturated sodic alkaline magmatism with a crustal component represented by peraluminous granites volcanic deposits from bottom to top are made mostly of volcanogenic sedimentary deposits succeeded by basic to intermediate lava and pyroclastic flows of shoshonitic affinity followed by intermediate and acid lava flows and ignimbrites of sodic alkaline affinity the last volcanic event is represented by basalt pahoehoe flows probably of mildly alkaline sodic affinity

ages u pb shrimp and la icpms and stratigraphic evolution of the neoproterozoic volcano sedimentary successions from the extensional camaqua basin southern brazil abstract during the ediacaran southern brazil was the site of multiple episodes of volcanism and sedimentation which are best preserved in the 3000 km2 camaqua basin the interlayered sedimentary and volcanic rocks record tectonic events and paleoenvironmental changes in a more than 10 km thick succession in this contribution we report new u pb and sm nd geochronological constraints for the 605 to 580 ma bom jardim group the 570 ma acampamento velho formation and a newly recognized 544 ma volcanism depositional patterns of these units reveal the transition from a restricted fault bounded basin into a wide shallow basin the expansion of the basin and diminished subsidence rates are demonstrated by increasing areal distribution and compressed isopachs and increasing onlap of sediments onto the basement to the west the sm nd isotopic composition of the volcanic rocks indicates mixed sources including crustal rocks from the adjacent basement both neoproterozoic and paleoproterozoic sources are indicated for the western part of the basin whereas only the older paleoproterozoic signature can be discerned in the eastern part of the basin

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

experimental high pressure granulites some applications to natural mafic xenolith suites and archean granulite terranes high pressure granulite assemblages have been produced as residues in partial melting experiments on a natural alkalic basalt amphibolite between pressures of 12 and 18 kbar in particular at 18 kbar partial melting of the hornblende plagioclase quartz assemblage under fluid absent conditions produces garnet clinopyroxene new albitic plagioclase melt seismic velocities v p are estimated from the modal data for the experimental assemblages and range from 6 90 km s for hornblende bearing residues to 7 62 for the dominantly garnet clinopyroxene residues these values are typical for rock types in the lowermost crust transitional to mantle the experimental results help place additional pressure temperature a h 2 o constraints on the source region for the natural high pressure granulites the experimental residue assemblage formed at 18 kbar has been described in natural xenolith suites from the delegate pipes in australia where the pipes intrude upper ordovician and lower devonian continental crust and in the bearpaw mountains montana where the xenolith bearing magmas intrude older crust of archean age the combination of these data shows that the xenoliths may indeed represent lowermost continental crust and furthermore helps interpret the nature of the crust mantle boundary in these areas the delegate pipes xenoliths suggest that the crust mantle boundary may be the site for partial melting and assimilation whereas the bearpaw mountains samples indicate that magmatic underplating may have been a major process in generating thick continental archean crust the experimental data and bearpaw mountains xenoliths suggest that the large range of rock types found in archean granulite terranes may not be representative of the lowermost continental crust

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

linear interference and the northern annular mode response to tropical sst forcing sensitivity to model configuration 1 interannual variability in tropical sea surface temperatures ssts associated with the el nino southern oscillation is linked to teleconnections with the northern annular mode nam previous work highlighted that the sign and amplitude of the nam response to tropical ssts are controlled by the total wave activity entering the subpolar stratosphere which depends on the linear interference of planetary wave anomalies with the climatological stationary wave field this study uses multiple configurations of atmospheric general circulation models to assess the robustness of these linkages to details of the tropical sst forcing and model configuration across 23 cases with idealized sst forcing the amplitudes of the tropical and extratropical wave responses are found to scale approximately linearly with forcing strength but wave amplitude alone is not sufficient to predict the nam response instead the spatial structure of the wave response and hence the linear interference provides the best explanation of the nam response in all cases linear interference explains most of the total wave activity response even in cases with stronger nonlinear contributions due to consistent cancellation between quasi stationary wave nonlinearity and nonlinearity arising from transient waves within this limited set of experiments there is no evidence for a consistent sensitivity of the nam response to horizontal resolution or to vertical resolution in the stratosphere these findings reveal that linear interference provides a robust and reproducible mechanism linking midlatitude wave responses to zonal mean circulation nam responses across a wide variety of forcing cases

linear and nonlinear winter atmospheric responses to extreme phases of low frequency pacific sea surface temperature variability this study examines northern hemisphere winter djfm atmospheric responses to opposite strong phases of interdecadal low frequency lf pacific sea surface temperature sst forcing which resembles el nino southern oscillation enso on a longer time scale in observations and gfdl and cam4 model simulations over the pacific north america pna sector linear observed responses of 500 hpa height z500 anomalies resemble the pna teleconnection pattern but show a pna like nonlinear response because of a westward z500 shift in the negative lf relative to the positive lf lf phase significant extratropical linear responses include a north atlantic oscillation nao like z500 anomaly a dipole like z500 anomaly over northern eurasia associated with warming over mid high latitude eurasia and a southern annular anomaly pattern associated with warming in southern land areas significant nonlinear z500 responses also include a nao like anomaly pattern models forced by lf and lf sst anomalies reproduce many aspects of observed linear and nonlinear responses over the pacific north america sector and linear responses over southern land but not in the north atlantic european sector and eurasia both models simulate pna like linear responses in the north pacific north america region similar to observed but show larger pna like lf responses resulting in a pna nonlinear response the nonlinear pna responses result from both nonlinear western tropical pacific rainfall changes and extratropical transient eddy feedbacks with lf tropical pacific forcing only lftp and lftp climatological sst elsewhere cam4 simulates a significant nao response to lftp including a linear negative and nonlinear positive nao response

geochemistry and origin of granitic rocks scourian complex nw scotland concordant granite sheets from the granulite facies scourian complex n w scotland exhibit the following features 1 a common planar fabric with their host pyroxene granulites 2 the presence of an exsolved ternary feldspar phase 3 a low pressure water saturated minimum composition 4 k rb ratios 450 1 350 distinctly higher than most upper crustal granites but similar to the surrounding granulites 5 low absolute concentrations of the rare earth elements rees light ree enrichment and large positive eu anomalies

large ion lithophile element characteristics of an amphibolite facies to granulite facies transition at gruinard bay north west scotland abstract lewisian grey gneisses from gruinard bay north west scotland retain mineralogical and geochemical evidence for scourian horn blende granulite facies metamorphism and they may be used to assess current models of elemental depletion at granulite grade their immobile major and trace element geochemistry is indistinguishable from that of lewisian amphibolite and pyroxene granulite facies counterparts the k rb th and u contents of the gruinard bay gneisses are depleted relative to amphibolite facies gneisses but generally the abundances of these elements are above those of comparable pyroxene granulites u and th have reached an advanced stage of depletion but allanite appears to be crucial in maintaining significantly higher u and th abundances at gruinard bay than in pyroxene granulites k and rb loss is less extreme and depends on the stability of the rock forming minerals k feldspar biotite and amphibole early removal of k and rb has resulted in a small rise in k rb but further preferential rb loss would have been required to generate the characteristically high k rb ratios of lewisian pyroxene granulites the residence of u and th in the accessory minerals of granulite facies gneisses which are often correlated with the residua of intracrustal partial melting renders unlikely their extreme incompatibility required by such models even if such phases are ignored high mineral melt partition coefficients for silicic melts argue against partial fusion as an efficient depletion mechanism on the other hand the advanced stage of u and th depletion reached in gruinard bay gneisses which were still partly hydrous severely restricts the role played by co2 dominated fluids and a hydrous medium is preferred

juvenile accretion at 750 700 ma in southern brazil a revista economic geology nao autoriza a publicacao de seus artigos em repositorios institucionais

lewisian gneiss geochemistry and archaean crustal development models abstract the geochemistry of lewisian amphibolite facies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulite facies gneisses the results show that there are no significant differences between laxfordian amphibolite facies and scourian granulite facies gneisses in terms of ree and other immobile trace elements at equivalent silica levels although the mobile radioactive heat producing elements k rb th u are significantly lower in the granulites in both types the basic gneisses have moderately fractionated ree patterns while the intermediate and acid gneisses have strongly fractionated ree patterns with low heavy ree abundances and decreasing levels of total ree with increasing sio 2 the most silicic gneisses develop large positive europium anomalies these gross chemical similarities between gneisses from intermediate amphibolite facies and lower granulite facies crustal levels constrain models for the evolution of the archaean crust the depletion of k rb cs th and u in granulites but not other incompatible trace elements cannot be explained by magmatic processes the positive eu anomaly in the more siliceous gneisses of both facies is a function of the primary processes of crustal generation and not secondary processes such as intracrustal melting or fractional crystallisation fractionation of radioactive heat producing elements from other trace elements is a result of granulite facies metamorphism with these elements being removed by an active fluid phase the apparent lack of partial melting in lower crustal granulites suggests a model for archaean crustal growth largely through underplating by primary tonalitic magmas

petrology and geochemistry of the neoproterozoic guaxupe granulite facies terrain southeastern brazil abstract geochemical and oxygen isotopic data on the neoproterozoic granulite facies rocks enderbites charnockite and charnokitic augen gneisses of guaxupe brazil are assembled geochemical discrimination function calculations show an igneous origin for majority of the rock types in the area major and trace element data especially ree are similar to tonalite and granodiorite oxygen isotope composition for charnockitic gneisses and mafic granulites yield 18o values in the range of 8 8 to 11 and fall in the range of quartzofeldspathic rocks of medium to high grade terrains elsewhere a small scale variation of 18o values compatible with the chemical data imply the preservation of pre metamorphic oxygen isotope compositions minimum peak pressure temperature conditions are 8 5 kbar and 850 c the high grade metamorphism did not appear to have altered significantly the geochemical and oxygen isotope compositions of the protoliths approximately 2 5 kbar of pressure decrease accompanied by 200 c cooling has been recorded for a portion of the cooling path the p t path is consistent with a single event namely the formation and uplift of the guaxupenappe in the neoproterozoic brasiliano cycle