age and origin of the ardal dike complex sw norway false isochrons incomplete mixing and the origin of caledonian granites in basement nappes 1 granitic dikes intruding the upper thrust sheets of the jotun nappe complex southwest norway previously assigned a sveconorwegian age based on rb sr data are redated to 427 1 ma by u pb the erroneous rb sr age can be explained by mixing of magmas with different isotopic compositions similar geochemical signatures evidence of sr mixing inherited proterozoic zircons and synkinematic modes of emplacement are also seen in silurian granites in the lifjorden complex as well as in the lindas nappe and the totland unit of the bergen arc complex we propose that these granites are related and derived from anatexis of rb poor sediments of baltica affinity overridden by the nappes during scandian thrusting this interpretation is compatible with the presence of the granites in nappes of both oceanic and of continental affinities and their absence in the autochthonous basement

global climatic anomalies associated with extremes in the southern oscillation abstract composite temperature and precipitation anomalies during various stages of an event in the southern oscillation so have been computed for several hundred stations across the globe large regions of coherent significant signals are shown to exist for both extremes of the so with warm event signals generally opposite to those during cold events in addition during the year preceding the development of an event in the so year 1 climatic anomalies tend to be opposite to those during the following year year 0 this confirms that the biennial tendency of the so over the pacific indian ocean sectors is also present in more remote regions with climatic signals related to the so many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes

sedimentary recycling in arc magmas geochemical and u pb hf o constraints on the mesoproterozoic suldal arc sw norway the hardangervidda rogaland block within southwest norway is host to 1 52 to 1 48 ga continental building and variable reworking during the 1 1 to 0 9 ga sveconorwegian orogeny due to the lack of geochronological and geochemical data the timing and tectonic setting of early mesoproterozoic magmatism has long been ambiguous this paper presents zircon u pb hf o isotope data combined with whole rock geochemistry to address the age and petrogenesis of basement units within the suldal region located in the centre of the hardangervidda rogaland block the basement comprises variably deformed grey gneisses and granitoids that petrologically and geochemically resemble mature volcanic arc lithologies u pb ages confirm that magmatism occurred from 1 521 to 1 485 ma and conspicuously lack any xenocrystic inheritance of distinctly older crust hafnium isotope data range from ehf initial 1 to 11 suggesting a rather juvenile magmatic source but with possible involvement of late palaeoproterozoic crust oxygen isotope data range from mantle like 18o 5 to elevated 10 suggesting involvement of low temperature altered material e g supracrustal rocks in the magma source the hf o isotope array is compatible with mixing between mantle derived material with young low temperature altered material oceanic crust sediments and older low temperature altered material continent derived sediments this combined with a lack of xenoliths and xenocrysts exposed older crust afc trends and s type geochemistry all point to mixing within a deep crustal magma generation zone a proposed model comprises accretion of altered oceanic crust and the overlying sediments to a pre existing continental margin underthrusting to the magma generation zone and remobilisation during arc magmatism the geodynamic setting for this arc magmatism is comparable with that seen in the phanerozoic e g the sierra nevada and coast range batholiths with compositions in the suldal sector reaching those of average upper continental crust as within these younger examples factors that drive magmatism towards the composition of the average continental crust include the addition of sedimentary material to magma source regions and delamination of cumulate material underthrusting of sedimentary materials and their subsequent involvement in arc magmatism is perhaps a more widespread mechanism involved in continental growth than is currently recognised finally the suldal arc magmatism represents a significant juvenile crustal addition to sw fennoscandia

the exeter group south devon england a contribution to the early post variscan stratigraphy of northwest europe the lower part of the post variscan succession around exeter south devon england comprises some 800 m of breccias with subordinate sandstones and mudstones which rest upon devonian and carboniferous rocks folded during the variscan orogeny and are overlain disconformably by the aylesbeare mudstone group early triassic these deposits comprise the most westerly of the early post variscan successions preserved onshore in northwest europe and lie to the south of the variscan deformation front they are assigned to the exeter group new term geochronological and palaeontological studies in conjunction with detailed geological mapping show that the constituent formations comprise a lower late carboniferous early permian sequence separated from an upper late permian sequence by an unconformity which represents an hiatus with a duration of at least 20 m y the lower sequence contains volcanic rocks dated at between 291 and 282 ma early permian and pre dates intrusion of the nearby dartmoor granite 280 ma in the overlying palynologically dated late permian sequence older breccias contain clasts of the dartmoor granite aureole rocks and younger ones contain clasts of that granite the lower sequence occurs mainly within the crediton trough an east west trending partly fault bounded sedimentary basin that probably formed by extensional reactivation of a variscan thrust breccias in this sequence formed largely on alluvial fans the common occurrence of debris flows and a down fan passage from gravity flows into fluvially deposited sediments is typical of deposition on semi arid fans the upper late permian sequence is more widespread but includes similar deposits overlain at the top of the exeter group by aeolian dune and interdune deposits correlation within the laterally variable facies associations which comprise these sequences has been achieved using a combination of sedimentary facies analysis sedimentary geochemistry and petrographical and geochemical clast typing the stratigraphy revealed within the exeter group is broadly comparable with that recognized in the early post variscan rotliegend successions elsewhere in europe this similarity may however be deceptive the upper part of the exeter group may be coeval with the zechstein and apparently correlatable major unconformities in the group and the rotliegend may reflect different events in the variscan fold belt and variscan foreland areas respectively

subaqueous outwash fan and esker sandstones in the permo carboniferous dwyka formation of south africa abstract four sandstone facies were defined in a 300 m thick diamictite member of the glacigene permo carboniferous dwyka formation the laterally persistent type a sandstones comprising quartz arenite are conformable to the bedding of the diamictite and are unreformed they are interpreted as subaqueous outwash fan deposits sandstone facies b also quartz arenites occurs intermittently along bedding planes in the diamictite and shows soft sediment deformation it represents subaqueous segmented outwash fan deposits which were primarily deformed by density loading of the soft diamicton the highly irregular type c sandstones comprise quartz and lithic arenites and wackes are randomly distributed in the diamictite and are deformed they ale interpreted as esker and esker delta deposits and rafted lumps of frozen meltwater sands deformed by overriding ice or density loading of the diamicton facies d consists of quartz and lithic arenites and represents clastic dikes and diapiric injections formed by density loading of waterlogged meltwater sand the three diamictite subfacies associated with the sandstones were deposited in open water by iceberg rafting suspension settling and debris flow by a combination of lodgement and melt out processes below grounded ice and below an ice shelf by debris rain suspension settling and slope failure the outwash fan deposits esker deltas clastic dikes and diapiric injections are confined to those parts of the basin covered by open water and the ice shelf the esker deposits formed in areas overlain by grounded ice episodic advance of the ice lobes and oscillation of the ice grounding line eroded the fan sediments and also contributed to the deformation of the sand bodies

the principal nonseasonal modes of variation of global sea surface temperature abstract thirty five million ship reports for the period 1949 79 have been used to construct global monthly mean sea surface temperature fields for 5 5 latitude longitude regions the monthly means have been subjected to eigenvector analysis to bring out the nonseasonal modes of variation the el nino mode is the most important and its eigenvector time series is identical to that found previously by weare et al for the pacific alone addition of data from the other oceans adds unexplained variance so that the percentage of the variance explained by the el nino mode is smaller in the global case than for the pacific alone the second most important eigenvector pattern shows evidence of a cooling trend for the north pacific and north atlantic in the 1964 79 period this is in agreement with previous work an zonal mean sea surface temperature by the authors with recent work on the north pacific by douglas et al and with a polar cap cooling in the lower troposphere for the same period reported by boer

glacial and rocky shore dynamics of the karlebotn monadnocks late neoproterozoic of northern norway located near the village of karlebotn in east finnmark norway a cluster of six gneissic monadnocks is unconformably surrounded by weakly metamorphosed sandstone strata of late neoproterozoic age in the smalfjord formation differentiated by faults the monadnocks were further sculpted by a glacier that flowed through a coastal valley concordant with the present day varangerfjorden the largest of the monadnocks is 337 m long and 167 m wide there remains ample evidence of glacial activity associated with this feature relict lodgement tillites are preserved on the west side of the monadnock flowtillites on the steep surfaces of the north and southwest sides and a small esker directly on top the valley was later inundated due to glacial eustacy and the karlebotn monadnocks became an archipelago in a shallow estuary of a broad fjord interpretation of exposed versus sheltered rocky shores on opposite sides of the largest monadnock island is supported by mineralogical variations in basal strata along t

climatology extremes in the indian ocean in contrast to the atlantic and pacific oceans the indian ocean has seemed to manifest little coherent behaviour in the variability of such parameters as water temperature and rainfall now however two studies identify a so called dipole mode in which the distribution of ocean temperature can be related to rainfall patterns in east africa and indonesia

atmospheric hydrospheric mechanisms of climate anomalies in the western equatorial indian ocean atmosphere ocean mechanisms of rainfall anomalies at the coast of eastern africa are studied using long term ship observations in the indian ocean surface current measurements subsurface casts upper air analyses by the european centre for medium range weather forecasts rain gauge series in eastern africa and india and an index of the southern oscillation so the high so phase being defined by anomalously high low pressure at tahiti darwin the causalities of precipitation anomalies at the coast of eastern africa differ for the two rainy seasons centered on april may and october november and only the latter is strongly related to the so in the high so phase april may pressure is low over the entire indian ocean domain whereas in october november pressure is high in the west and low in the east concomitantly surface waters are anomalously cold in the west and strong westerlies sweep the equatorial zone of the indian ocean eastern african rainfall anomalies are related to the so through a combination of cooperative mechanisms that function most effectively in the boreal autumn rainy season of eastern africa 1 equatorial westerly winds are conducive to lower tropospheric divergence over equatorial east africa and in the high so phase these are accelerated especially in october november owing to the anomalous eastward pressure gradient 2 the equatorial westerly winds drive the eastward equatorial jet in the upper hydrosphere which entails cold water upwelling in the western extremity of the basin where sea surface temperature further hydrostatically affects the zonal pressure gradient and thus feeds back into the equatorial westerly winds 3 in addition cold water anomalies in the western indian ocean most pronounced in october november during the high so phase also suppress convection 4 in the high so phase the indian summer monsoon tends to be strong leaving behind an anomalously cold western indian ocean which in turn feeds into mechanisms 1 to 3 the eastward equatorial jet thus has a role to play in feedback mechanisms contributing to the anomalies of the boreal autumn rains at the coast of eastern africa

ordovician early silurian intrusive rocks in the northwest part of the upper allochthon mid norway plutons of an iapetan volcanic arc complex

zonal circulations over the equatorial indian ocean abstract the ncep ncar 1958 97 upper air dataset and surface observations have been analyzed for evidence of zonal vertical circulations along the indian ocean equator and their role in climatic variability the long term mean upper tropospheric circulation is dominated in boreal winter by divergent outflow from the southern indian ocean northwestward into southern asia and in summer from southern asia southwestward into the southern hemisphere in boreal autumn only divergent easterlies blow from indonesia along the equator into an upper tropospheric convergence band over east africa and only then a closed zonal vertical circulation cell materializes along the indian ocean equator between the centers of ascending motion over indonesia and of subsidence over equatorial east africa and featuring westerlies in the lower layers the boreal autumn zonal vertical circulation varies interannually a regime of intense circulation features accelerated equatorial surface westerlies enhanced subsidence and d

low frequency sea surface temperature and wind variations over the indian and pacific oceans the wind and temperature fields over the indian and pacific oceans have been analyzed to study the coupling between the two oceans on the time scale of the southern oscillation the analysis shows the propagation of zonal wind anomalies from the western pacific ocean toward the date line together with the displacement of a pool of warm water there is some indication of a zone of convergence over the equatorial indian ocean the results seem to rule out a direct propagation of a signal from the indian ocean toward the pacific ocean as the signal in the former ocean lags that in the latter

metasomatism and the crystallization of zircon megacrysts in archaean peridotites from the lewisian complex nw scotland zircon megacrysts are locally abundant in 1 40 cm thick orthopyroxenite veins within peridotite host rocks in the archaean lewisian gneiss complex from nw scotland the veins formed by metasomatic interaction between the ultramafic host and si rich melts are derived from partial melting of the adjacent granulite facies orthogneisses the interaction produced abundant orthopyroxene and within the thicker veins phlogopite pargasite and feldspathic bearing assemblages two generations of zircon are present with up to 1 cm megacrystic zircon and a later smaller equant population located around the megacryst margins patterns of zoning rare earth element abundance and oxygen isotopic compositions indicate that the megacrysts crystallized from crustal melts whereas the equant zircon represents new neocryst growth and partial replacement of the megacryst zircon within the ultramafic host both zircon types have u pb ages of ca 2464 ma broadly contemporaneous with granulite facies events in the adjacent gneisses zircon megacrysts locally form 10 of the assemblage and may be associated to zones of localized nucleation or physically concentrated during movement of the siliceous melts their unusual size is linked to the suppression of zircon nucleation and increased zr solubility in the si undersaturated melts the metasomatism between crustal melts and peridotite may represent an analog for processes in the mantle wedge above subducting slabs as such the crystallization of abundant zircon in ultramafic host rocks has implications for geochemistry of melts generated in the mantle and the widely reported depletion of high field strength elements in arc magmas

indian ocean warming of 1997 1998 the indian ocean underwent substantial changes in 1997 1998 the observations show not only the appearance of a dipole mode in the tropical region but also a persistent basin scale warming we present in this study an analysis of the basin scale sea surface temperature sst variations during 1997 1998 using satellite observations in situ temperature measurements and national centers for environmental prediction reanalyses we find that the indian sst anomaly peaks occurred at two periods i e november december january coinciding with the nino3 peak and the following april may june and were phase locked to the indian ocean seasonal cycle the changes of sst in the equatorial ocean were related to a coupled interaction between the atmosphere and the ocean oceanic upwelling in the east and downwelling in the west played a major role in giving rise to the sst anomalies associated with the dipole mode structure the upwelling off the coast of sumatra elevated the regional thermocline by more than 80 m in december 1997 on the other hand the changes of sst in the southern indian ocean were largely induced by the changes of local latent flux during boreal fall winter of 1997 the southeasterly trades were displaced and abnormally prolonged in their northernmost equatorial position this shifted the center of the trades toward the equator weakened the winds in the central southern ocean reduced the latent heat flux in the region and subsequently induced a surface warming the total change of the sst anomalies integrated over the two periods july december 1997 and january may 1998 were explained well by the same period latent flux integral in both intensity and pattern the cross basin upper ocean temperature sections show that the extratropical warming was rather uniformly distributed in the upper 60 m further supporting the role of mixed layer processes in the warming

dynamics of the surface wind field over the equatorial indian ocean the annual cycle and interannual variability of the equatorial westerlies over the indian ocean are examined in the context of the equations of motion using long term surface ship observations eastward pressure gradient along the equator may accelerate equatorial westerlies but the process is more intricate the south indian ocean trade winds can recurve in the southern hemisphere only with an eastward pressure gradient this is counteracted by the coriolis acceleration directed at right angles to the left of the motion with weak trades and strong eastward pressure gradient the flow can recurve at relatively high southern latitudes thus allowing a broad equatorial zone in which westerlies can develop in the annual cycle the southern indian ocean high and trade winds are closest to the equator and strongest in austral winter when however the eastward pressure gradient in the equatorial zone is also steepest accordingly the latitude of flow recurvature in the southern trade winds stays farthest away from the equator in boreal spring and autumn consequently the equatorial westerlies peak in these short transition seasons the boreal autumn equatorial westerlies are the surface manifestation of a powerful zonal circulation cell along the indian ocean equator the interannual variability of boreal autumn is characterized by weak westerlies accompanying a slack zonal pressure gradient and strong southern trade winds with recurvature near the equator such an ensemble of circulation departures is characteristic of abundant rainfall in east africa and deficient precipitation in indonesia copyright 2004 royal meteorological society

diagnosing the 2005 drought in equatorial east africa abstract equatorial east africa suffered severe drought during its 2005 short rains centered on october november the circulation mechanisms of such precipitation anomalies are examined using long term upper air and surface datasets and based on diagnostic findings from earlier empirical investigations the steep eastward pressure gradient is conducive to fast westerlies over the central equatorial indian ocean surface manifestation of a powerful zonal circulation cell with subsidence over east africa and ascending motion over indonesia with fast westerlies rainfall in east africa is deficient and they tend to be accompanied by anomalously cold waters in the northwestern and warm anomalies in the southeastern extremity of the equatorial indian ocean basin without any seesaw between these domains in october november 2005 pressure in the west was anomalously high entailing a steep eastward pressure gradient along the equator conducive to fast westerlies and further symptomatic of the zonal ci

indian ocean dipolelike variability in the csiro mark 3 coupled climate model abstract coupled ocean atmosphere variability in the tropical indian ocean is explored with a multicentury integration of the commonwealth scientific and industrial research organisation csiro mark 3 climate model which runs without flux adjustment despite the presence of some common deficiencies in this type of coupled model zonal dipolelike variability is produced during july through november the dominant mode of variability of sea surface temperature resembles the observed zonal dipole and has out of phase rainfall variations across the indian ocean basin which are as large as those associated with the model el nino southern oscillation enso in the positive dipole phase cold sst anomaly and suppressed rainfall south of the equator on the sumatra java coast drives an anticyclonic circulation anomaly that is consistent with the steady response gill model to a heat sink displaced south of the equator the northwest southeast tilting sumatra java coast results in cold sea surface temperature

ordovician faunas island arcs and ophiolites in the scandinavian caledonides ordovician faunal data from the scandinavian caledonides is tested with new geochemical information from zircons to give u pb ages and source origins of volcanic arc and ophiolite sequences early ordovician arenig llanvirn low latitude toquima table head faunas from the upper upper allochthon are associated with an island arc system formed adjacent to laurentia contemporaneous mafic magmas were contaminated by crustal material during subduction and associated granites contain inherited zircons of archaean age the nearest source for such rocks is on the laurentian rather than the baltic side higher latitude celtic province faunas from the upper upper allochthon are from one insular site accessible to forms from both laurentia and baltica the late ordovician low latitude holorhynchus and subtropical hirnantia faunas occur in overstep sequences above deeply eroded early ordovician arc complexes the transgression appears to be coeval with a second generation of spreading related complexes single detrital zircons from sediments show sources from archaean proterozoic and early ordovician terranes this suggests that deposition was in a basin situated along the same continental margin laurentia to which the early ordovician ophiolite arc sequences had already become accreted the late ordovician faunas link both laurentia and baltica at a time of narrowing of lapetus the new geochemical data together with the faunal information is supported by recent palaeomagnetic studies

the sognefjell volcanic subvolcanic complex a late sveconorwegian arc imbricated in the central norwegian caledonides abstract the sognefjell volcanic subvolcanic complex is a composite unit underlying the jotun nappe complex in the southern norwegian caledonides the identity and origin of the complex have been highly debated in past decades one interpretation considering the rocks to be highly deformed orthogneisses of the jotun nappe complex and the other extreme considering them to be partly of volcanic origin and defining a caledonian suture in this study some critical components of the complex have been dated by u pb yielding ages of 961 11 ma for gabbro and 949 4 ma for a tonalite a tuffite includes euhedral zircon crystals with ages of 985 to 955 ma suggesting derivation from the same magmatic complex zircon in an orthogneiss points instead to an older age close to 1600 ma suggesting that this is a sliver of the jotun nappe complex a thin straight pegmatite cutting mafic gneiss is 949 3 ma titanite grains in the various rocks range in age from about 970 to 890 ma demonstrating that the dominant metamorphism was sveconorwegian with minimal resetting in spite of the likely caledonian deformation the new observations combined with published data support the notion that these rocks are of volcanic subvolcanic origin but show that they are late sveconorwegian not caledonian as originally envisaged they likely developed in an arc complex at the margin of baltica and possibly within the realm of the asgard sea arc magmatism was coeval with lower crustal processes in parts of the baltic craton that would eventually become caledonian nappes

warming trend of the indian ocean sst and indian ocean dipole from 1880 to 2004 the state of the indian ocean dipole representing the sst anomaly difference between the western and southeastern regions of the ocean is investigated using historical sst reconstructions from 1880 to 2004 first the western and eastern poles of the sst based dipole mode index are analyzed separately both the western and eastern poles display warming trends over this period particularly after the 1950s the western pole tends to be anomalously colder than the eastern pole from 1880 to 1919 whereas in the interval 1950 2004 the sst anomalies over the western pole are comparable to those over the eastern pole though there are occasional outliers where the eastern pole is anomalously colder than the western pole the tendencies of the occurrences of positive and negative dipole events in september november show three distinct regimes during the period analyzed in 1880 1919 negative dipole events associated with la nina events occur more frequently than positive events in 1920 49 some weak positive events occur relatively independently of el nino events over the pacific the period of 1960 2004 is characterized by strong and frequent occurrences of positive events associated with el nino events

volatile phase fluxed anatexis of metasediments during late caledonian ophiolite obduction evidence from the sogneskollen granitic complex west norway in the west norwegian caledonides minor granitic sheets were intruded during obduction of the c 443 ma solund stavfjord ophiolite complex the sogneskollen granitic complex is the largest intrusive complex and consists of several minor lenses and one larger lens of granodiorite the sogneskollen granitic complex samples generally have high ba sr and na 2 o very low y values nd 420 ma values c 7 to 10 1 and 87 sr 86 sr 420 ma ratios of 0 70437 0 70705 the ree patterns are strongly hree depleted and la yb n varies from 0 3 to 36 most samples display small positive eu anomalies but those that are most fractionated have small negative anomalies the main part of the sogneskollen granitic complex is a white composite granodiorite which is intruded by a suite of grey biotite granite dykes it is suggested that this and other similar granitic sheets in the area most probably formed by melting of sediments in the presence of a h 2 o bearing volatile phase during obduction of the ophiolite the quartzofeldspathic source sediments most probably contained detritus from long term rb depleted lower continental crust and from an island arc the sediments were deposited in large amounts in the marginal basin now represented by the solund stavfjord ophiolite complex during obduction the sediments were buried beneath the hot overriding ophiolite complex and the associated island arc and yielded granitic magmas during partial melting

relative role of dynamic and thermodynamic processes in the development of the indian ocean dipole an ogcm diagnosis 1 the relative role of oceanic dynamics and surface heat fluxes in the initiation and development of the indian ocean dipole was investigated by analyzing results from an oceanic general circulation model the model was forced by observed surface wind stress and heat flux fields for 1958 1997 the results show that it was capable of reproducing observed dipole events over the tropical indian ocean the diagnosis of the mixed layer heat budget indicates that the sst anomaly ssta in the east pole is primarily induced by anomalous surface latent heat flux and vertical temperature advection whereas in the west pole it is mainly caused by meridional and vertical temperature advection anomalies in both regions shortwave radiation anomalies tend to damp the ssta the ocean rossby waves are essential in linking the anomalous wind and sst off sumatra and subsurface temperature variations in southwest indian ocean

uniformitarianism as a guide to rocky shore ecosystems in the geological record literature on pleistocene and neogene rocky shores is reviewed from a uniformitarian perspective to assess the fidelity of physical and biological information entrained in the geological record through present day processes coverage by latitude spans tropical to subarctic shores variations in paleotopography are illustrated by unconformities between sedimentary accumulations and rocks of igneous or non igneous origin former rocky shores occur across a range of geographic scales that include i spot localities ii embayments with continuous transition from exposed outer to protected inner shores and iii entire islands with windward and leeward shores differences in rate and mag nitude of sea level change affect rocky shore physiography terrace deposits characterize the pleistocene but ramp de posits typify older neogene shores on average species with hard parts account for about 50 of the modern rocky intertidal fauna on a regional basis regardless of latitude biodiversity is highest in mid latitudes fixed organisms with encrusting wedging or boring habits corals barnacles oysters other bivalves and vermetid gastropods show high potential for fossilization in growth position mobile organisms that cling to rocks gastropods crabs and echinoids suffer post mortem transport but may be immured within neptunian dikes or interstices among cobbles and boulders at best localized fossil deposits from the pleistocene reflect 30 of the biodiversity of skeletonized organisms tabulated from modern rocky shores on a regional basis uniformitarianism provides little insight into the diversity of soft bodied organisms excluding stromatolites that joined the ecosystem in precambrian times and the extent to which soft bodied organisms dominated shore life through later times

interaction of the monsoon and pacific trade wind system at interannual time scales part iii a partial anatomy of the southern oscillation abstract studies of surface wind fields sea surface temperature sst precipitation and sea level pressure in the tropical band extending 30 of the equator from africa to south america led to the following conclusions the southern oscillation el niflo and climatic variations in the monsoon system are all part of one global scale phenomenon the new information is that this phenomenon appears in the sea level pressure field to have a strong propagating component that appears first in the northern indian ocean and moves eastwardinto the eastern pacific similar propagation of information was found in the surface wind field and equatorial precipitation regimes these same conditions were amply demonstrated during the 1982 83 event and so it may be concluded that the evolution of that event bears many similarities to those in the historical record studies referred to in this paper in the surface wind field of the equatorial wave guide the large scale signal appears to take the form of a forced kelvin

evidence for a glacial origin of neoproterozoic iii striations at oaibaccannjar ga finnmark northern norway the origin of the famous late precambrian striated pavement at oaibaccannjar ga bigganjargga northern norway remains controversial most investigators have accepted a glacial formation but some prefer a soft sediment mechanism however a newly discovered c 2 5 mm thick zone of brecciation under rare polished striations indicates a hard substrate during formation and thus a glacial origin for the striations other points indicating that the striations formed in a hard substrate are 1 the striated platform in the veidnesbotn formation is c 150 ma older than the overlying diamictite smalfjord formation having been buried to c 2 5 km depth cementation should have started before smalfjord times 2 the marked irregularity of the sub smalfjord formation palaeotopography on skjaholmen 3 the presence of rounded veidnesbotn formation boulders in the diamictite above the striations imprints of clasts appearing to lie across the striations are re interpreted as relicts of mud flakes within the veidnesbotn formation which were cut across and quarried out during pavement formation the origin of the overlying diamictite tillite vs debris flow is not constrained by the presence of glacial striations and most probably was deposited some time after striation formation

dating the lower crust by ion microprobe ion microprobe uthpb ages of zircons from granulite facies lower crustal xenoliths from north queensland australia correlate well with the ages of major orogenic episodes manifest at the earth s surface about half of the xenoliths contain proterozoic zircons which are similar in age to the episodes of high grade metamorphism of the older surface rocks all the xenoliths contain late paleozoic zircons which show a real 100 ma range in206pb238 u ages from 320 to 220 ma which is attributed to granulite facies metamorphism followed by slow cooling in the deep crust the paleozoic zircon ages coincide in time with the prolonged episode of eruption of voluminous felsic ash flows and intrusion of high level granites in this region 320 270 ma mineral and melt inclusions in the zircons provide clues to the origin of some of the xenoliths and coupled with the age information can be used to infer the geological processes operating in the lower crust the zircons from two mafic xenoliths contain felsic and intermediate melt inclusions implying at least a two stage history for these rocks involving either partial melting of a more felsic protolith or crystal accumulation from an evolved melt some of the zircons from the felsic xenoliths contain co2 rich fluid inclusions indicating that those zircons grew during high grade metamorphism the isotopic and chemical data for the whole rock xenoliths show that they originate from a segment of the lower crust which is a heterogeneous mixture of supracrustal and mafic mantle derived lithologies the major orogenic event responsible for the formation of that crust occurred in the late paleozoic when proterozoic supracrustal rocks were emplaced into the lower crust possibly along thin skinned thrust slices this was accompanied by intrusion of high temperature mantle derived melts which caused partial melting of pre existing crust the most likely setting for such tectonism is a continental margin subduction zone

early palaeozoic peri gondwana terranes new insights from tectonics and biogeography following the late neoproterozoic early cambrian breakup of the supercontinent rodinia gondwana evolved as one of the principal continental masses on earth embracing most of south america africa australasia antarctica much of western europe and parts of asia around its margins were various other terranes that had varying tectonic and biogeographical affinities with the main continental block this book incorporates a series of reviews and multidisciplinary research papers that together explore the tectonic palaeogeographical and palaeobiogeographical evolution of the elements that made up the peri gondwanan collage the stratigraphical scope of the coverage embraces the late precambrian through early devonian providing a comprehensive overview of structural stratigraphical and biological evolution through this significant interval of earth history integration of these various processes throughout the volume will be of broad based interest to a wide range of geoscientists

the hardangerfjord shear zone in sw norway and the north sea a large scale low angle shear zone in the caledonian crust the hardangerfjord shear zone is a more than 600 km long low angle extensional structure that affects the south norway and north sea caledonides the ductile shear zone which shows total maximum onshore displacement of the order of 10 15 km is primarily a basement structure with an associated passive monoclinal fold structure of the overlying caledonian nappes deep seismic data indicate that the shear zone continues down to the lower crust 20 25 km at a dip of 22 23 where it appears to flatten and merge with the general lower crustal deformation fabric onshore the hardangerfjord shear zone consists of a system of hard linked ductile shear zone segments brittle faults the l rdal gjende fault system occur in the folded caledonian allochthons in the ne part of the hardangerfjord shear zone and reappear in the north sea these may represent a high level brittle response to the devonian development of the hardangerfjord shear zone but were reactivated during permo triassic and late jurassic extensional events a c 5 km thick package of seismic reflectors along the hardangerfjord shear zone is presumed to represent a mylonite zone which is too thick to be formed entirely by 10 15 km of devonian displacement hence the hardangerfjord shear zone is likely to be a proterozoic shear zone reactivated during devonian extension

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

ordovician life around the celtic fringes diversifications extinctions and migrations of brachiopod and trilobite faunas at middle latitudes during the early to mid ordovician marine life experienced an unprecedented rise in diversity at the species genus and family levels that firmly installed the suspension feeding benthos as the main component of the palaeozoic fauna the earlier ordovician was characterized by a wide dispersal of the continents together with a high frequency of microcontinents and volcanic arcs magmatic and tectonic activity was intense climates were warm and sea levels were high central to the entire diversification is the role of gamma inter provincial diversity and by implication the spread of the continents and frequency of island arcs and microcontinents a disparate group of continental fragments and island arcs loosely assigned to the celtic province contained distinctive shelly faunas that formed a testable biogeographical unit the celtic faunas are characterized by a large number of endemic brachiopod taxa some cosmopolitan forms and taxa at the beginning or end of their stratigraphical ranges the associated trilobite faunas are composed largely of wide ranging genera a few genera at the start of their stratigraphical range and some recently evolved taxa extending their geographical range the celtic province helped provide a burst of gamma diversity during the early stages of the ordovician radiation whereas the timing and position of the archipelagos associated with the celtic province may have provided a mechanism for the diachroneity associated with the diversification

evidence for a caledonian amphibolite to eclogite facies pressure gradient in the middle allochthon lindas nappe sw norway the proterozoic anorthosite mangerite charnockite complex dominating the lindas nappe in the scandinavian caledonides was locally eclogitized in the southwestern part of the nappe during the caledonian orogeny whereas only amphibolite facies assemblages are recorded in the rest of the nappe sveconorwegian granulites of anorthositic to jotunitic composition in the northernmost eclogite free exposures of the nappe exhibit large garnet phenoblasts ca 900 c that are fractured and partly replaced by a caledonian symplectitic amphibolite facies assemblage ca 515 c metamorphic zircon attributed to this garnet breakdown is dated by id tims u pb at 430 3 ma suggesting that the amphibolite facies overprint was coeval with the formation of eclogite 30 km further south probably implying that the section across the nappe represents a caledonian pressure gradient the rocks also preserve a complex sveconorwegian history including an age of 969 6 ma which we interpret as dating magmatic emplacement of jotunitic anorthositic portions of the complex 936 12 ma reflecting the granulite facies metamorphism and 908 16 ma representing a late generation of zircon best explained as having formed by metasomatic processes caledonian shearing severely deformed zircon grains in an amphibolite facies shear zone resetting their u pb systems and forming new ones hereby also demonstrating a case of resetting and recrystallization of low u zircon our data gained from diverse lithologies illustrate several processes involved in making and resetting zircon as well as indicate the contemporaneous evolution and similar origin of the lindas nappe and the jotun nappe complex

the seasonal development of an sst anomaly in the indian ocean and its relationship to enso abstract the seasonal development of the sea surface temperature sst anomaly in the indian ocean is investigated in relation to el nino southern oscillation enso using noaa optimally interpolated sst and ncep reanalysis data the result shows that the onset season of el nino affects the seasonal development of surface wind anomalies over the equatorial eastern indian ocean eeio these surface wind anomalies in turn determine whether the sst anomaly in the eeio evolves into the eastern pole of the dipole pattern in years when the dipole pattern develops surface zonal wind anomalies over the eeio switch from westerly to easterly in spring as la nina switches to el nino the seasonal zonal wind over the eeio also switches from westerly to easterly in spring and the anomalous wind strengthens seasonal wind from winter to summer stronger winds and resultant thermal forcings produce the negative sst anomaly in the eeio in winter and its amplitude increases in summer the sst anomaly becomes the ea

provenance and tectonic evolution of ganderia constraints on the evolution of the iapetus and rheic oceans we provide estimates for the width timing and rates of opening and closing of the iapetus and rheic oceans the evolution of which profoundly infl uenced paleozoic global paleogeography these estimates are primarily derived from the transfer of ganderia and avalonia from gondwana to laurentia which led to closure of the iapetus ocean and opening of the rheic ocean ganderia a long lived arc terrane separated from the paleo caribbean margin of amazonia at 505 ma with a latitudinal speed of 9 cm a northward initiating the rheic ocean as a backarc basin ganderia s trailing edge was reduced to 5 cm a following opening of a 600 800 km wide backarc basin within ganderia at 475 ma opening and closing of the iapetus ocean was largely driven by far fi eld stresses slab pull in some places and slab rollback in others

nonstationary enso precipitation teleconnection over the equatorial indian ocean documented in a coral from the chagos archipelago d 18 oc o f aporites coral from the chagos archipelago 71 e 5 s only after the mid 1970s a strong enso signal emerges in the d 18 oc during the analyzed period 1950 1994 in the 1970s the increasing sea surface temperature sst shifted the mean sst closer to the deep convection threshold at about 28 5 c enso related sst variability largely controls the deep convection and precipitation in the central equatorial indian ocean ceio when the sst is at this critical level the anomalies in the precipitation induce changes in the isotopic composition of the surface ocean waters the precipitation signal amplifies the sst signal in the coral d 18 oc and raises the correlation to enso the presented results have important implications for the reconstruction of enso indices from corals within the indian ocean citation timm o m pfeiffer and w c dullo 2005 nonstationary ensoprecipitation teleconnection over the equatorial indian ocean documented in a coral from the chagos archipelago geophys res lett 32 l02701 doi 10 1029 2004gl021738

glacial or non glacial origin for the bigganjargga tillite finnmark northern norway bigganjargga is the classic locality for the varangian ice age in northern scandinavia the presence of two sets of striations on the underlying quartzite basement has been taken as evidence for a glacial origin of the bigganjargga diamictite however soft sediment surface structures on the underlying sandstone indicate that it was not consolidated when the diamictite was emplaced together with structures in the diamictite this shows that the deposit formed as a debris flow moving northwestwards over an unconsolidated substrate there is no evidence for glacial origin or contribution for the diamictite material

a recipe for simulating the interannual variability of the asian summer monsoon and its relation with enso this study investigates how accurately the interannual variability over the indian ocean basin and the relationship between the indian summer monsoon and the el nino southern oscillation enso can be simulated by different modelling strategies with a hierarchy of models from an atmospherical general circulation model agcm forced by observed sst to a coupled model with the ocean component limited to the tropical pacific and indian oceans the role of heat fluxes and of interactive coupling is analyzed whenever sea surface temperature anomalies in the indian basin are created by the coupled model the inverse relationship between the enso index and the indian summer monsoon rainfall is recovered and it is preserved if the atmospherical model is forced by the ssts created by the coupled model if the ocean model domain is limited to the indian ocean changes in the walker circulation over the pacific during el nino years induce a decrease of rainfall over the indian subcontinent however the observed correlation between enso and the indian ocean zonal mode iozm is not properly modelled and the two indices are not significantly correlated independently on season whenever the ocean domain extends to the pacific and enso can impact both the atmospheric circulation and the ocean subsurface in the equatorial eastern indian ocean modelled precipitation patterns associated both to enso and to the iozm closely resemble the observations

interannual displacements of convection and surface circulation over the equatorial indian ocean the interannual variability of surface observations in the equatorial indian ocean is investigated from 23 years of ship reports 1954 1976 in october and november during certain years the monthly analyses show strong wind anomalies in the eastern and central equatorial indian ocean simultaneously cloud cover anomalies of opposite signs are observed in the eastern indian ocean and in the central indian ocean a linear analysis of heat induced circulation suggests that the surface wind anomalies are forced by anomalies of rainfall this circulation is probably dissipative with time scales in the range two to five days the reasons for the maintenance of anomalous circulations are not well known it is noted that during most el nino events in the pacific ocean anomalies are observed in the indian ocean however there are other years with the same anomalous pattern 1961 for example during the years with anomalously little cloudiness in the eastern indian ocean sea surface temperatures lower than normal are found in the eastern indian ocean this suggests that coupled air sea dynamics must be taken into account to understand the interannual variability

geochronology of caledonian metamorphic allochthons in the otta heidal region south norway tectonostratigraphic and palaeogeographical implications the caledonian appalachian belt formed in the early paleozoic by the assembly and dispersal of continental and oceanic crustal fragments of diverse provenance the characterization of these terranes and information on their origins are essential in reconstructing the course of the orogeny the region of northern gudbrandsdalen in norway is important for elaborating these questions as it represents a geological transition in architectural style and composition of the caledonian nappes and the meeting point of tectonic elements with diverse geological histories of both baltic and exotic origins in the past century this complexity has generated conflicting interpretations which we have tested with new mapping and isotope dilution thermal ionization mass spectrometry u pb dating the new data show the following 1 a metagabbro low in the tectonostratigraphy has an age of 1497 5 ma correlating with the espedalen complex of telemarkian 1550 1480 ma affinity 2 the structurally higher crystalline rudihoe mukampen suite was metamorphosed at high grade during the sveconorwegian orogeny mainly between 980 and 900 ma with older components pointing to a gothian 1700 1600 ma affinity 3 these ages and mapping indicate that the rudihoe mukampen suite is a lateral equivalent of the upper jotun nappe 4 the overlying dominantly metasedimentary steinho complex was metamorphosed in the ordovician at about 473 3 ma 5 both the rudihoe mukampen suite and steinho complex were intruded by trondhjemite dykes at 430 427 ma these units are structurally overlain by the lowest elements of the trondheim nappe complex which includes serpentinite lenses and conglomerates the products of hyperextension locally with ordovician fossils the new results dispel some of the problematic interpretations proposed earlier and represent new firm elements that will anchor future tectonic reconstructions of the caledonides in this region

mechanisms of climate anomalies in the equatorial indian ocean 1 building on earlier work on the interannual variability of the boreal autumn equatorial westerlies ueq over the indian ocean and concomitant rainfall anomalies at the coast of east africa and in indonesia the inherent circulation mechanisms are here explored further from long term surface and upper air data fast ueq and deficient east african rainfall come with positive sea level pressure p and negative sea surface temperature t departures in a domain w at the northwestern extremity and opposite departures in a domain e at the southeastern extremity of the equatorial indian ocean however there is no seesaw between w and e in either p or t and no indication of local forcing of t on p the large scale pressure field in particular the zonal pressure gradient along the equator and the south indian ocean pressure and southern tradewinds control the evolution of ueq fast ueq steepens the zonal temperature gradient thus tightening the inverse relationships between the zonal gradients of pressure and temperature the rainfall anomalies associated with the interannual variability of ueq surface manifestation of a zonal circulation cell along the indian ocean equator are favored by the kinematic and thermodynamic conditions in w and e thus with fast ueq the domain w features departure lower tropospheric divergence and subsidence and favored by the cold t and subsidence reduced precipitable water all conducive to deficient precipitation by contrast e has departure lower tropospheric convergence and ascending motion and favored by the warm t and ascending motion enhanced precipitable water in conjunction conducive to abundant rainfall the interannual variability of the boreal autumn equatorial westerlies dominated as it is by the large scale pressure field is crucial in the climate dynamics of the equatorial indian ocean region this leads to the question what controls the pressure pattern over the indian ocean basin

early ordovician terne linkages between oceanic and continental ternes in the central scandinavian caledonides the presence of a first order unconformity in the central part of the scandinavian caledonides linking together early ordovician late cambrian outboard oceanic ternes and the continental margin of baltic is of considerable importance for interpreting the geodynamic framework of the orogen this and other criteria for terne linkage are described together with implications for the regional tectonostratigraphic development in this segment of the caledonides

glacial influence on neoproterozoic sedimentation the smalfjord formation northern norway there is much debate regarding the intensity and geographic extent of glaciation during the neoproterozoic particularly in response to recent geochemical work suggesting that the neoproterozoic earth was at times ice covered from equator to poles the snowball earth hypothesis a detailed sedimentological analysis of the neoproterozoic smalfjord formation of northern norway was conducted in order to determine the extent and intensity of glacial influence on sedimentation in the tarmfjorden area the smalfjord formation consists of a stacked succession of diamictites interbedded with fine grained laminated mudstones containing rare outsized clasts diamictites and interbedded mudstones are interpreted as the product of subaqueous mass flows generated along the basin margin in the varangerfjorden area chaotically interbedded diamictites conglomerates and sandstones are overlain by a thick succession of stacked sandstone beds one diamictite unit at bigganjargga overlies a striated pavement the varangerfjorden outcrops appear to record deposition on a subaqueous debris apron although diamictites contain rare striated and faceted clasts suggesting a glacial sediment source their origin as subaqueous mass flows prevents the interpretation of ice mass form or distribution rare lonestones may be associated with floating ice in the basin which may be of glacial or seasonal origin glacial ice may have contributed poorly sorted glacial debris to the basin margin either directly or through fluvioglacial systems but there is no evidence of direct deposition by ice at varangerfjorden or tarmfjorden the overall fining upward trend identified in the smalfjord formation and overlying nyborg formation is consistent with depositional models of rift basin settings this fining upward trend the predominance of mass flow facies including breccias associated with scarps and the evidence for extensional tectonic activity in the region suggest that tectonic activity may have played an important role in the development of this neoproterozoic succession the smalfjord formation at tarmfjorden and varangerfjorden does not exhibit sedimentological characteristics consistent with severe glacial conditions suggested by the snowball earth hypothesis

circulation mechanisms of kenya rainfall anomalies abstract expanding earlier studies on the boreal spring and autumn rainy seasons in equatorial east africa pending challenges on the mechanisms of rainfall variability are investigated eastward pressure gradient and slack south indian ocean trade winds allow surface equatorial westerlies in spring and autumn complementing that upper tropospheric easterlies are required for the development of a zonal vertical circulation cell along the indian ocean equator because of the summer warming and high stand of upper tropospheric topography over south asia strong upper tropospheric easterlies over the tropical northern and equatorial indian ocean persist from summer into autumn thus allowing the development of a zonal vertical circulation cell by contrast the winter cooling entails low stand of upper tropospheric topography in the north thus hindering easterlies over the equator consequently an equatorial zonal circulation cell does not develop in boreal spring the equatorial zonal circulation cell

late orogenic sveconorwegian massif anorthosite in the jotun nappe complex sw norway and causes of repeated amcg magmatism along the baltoscandian margin the age and tectonometamorphic history of massif anorthosite in the jotun nappe complex sw norway were investigated by zircon and titanite u pb id tims the anorthosite contains sparse zircons showing complex u pb systematics reflecting events dated at 965 4 and 913 2 ma and a pronounced caledonian metamorphic overprint the oldest age is interpreted as the protolith age of the massif anorthosite we propose that the jotun anorthosite is related to 970 960 ma magmatism in the western gneiss region and coeval orogen perpendicular extension conversely a 930 ma high grade metamorphic event in the jotun nappe complex and the related lindas nappe is likely related to formation of the autochthonous ca 930 ma rogaland anorthosite complex we suggest that the two late to post orogenic amcg events reflect two instances of lithospheric foundering below the orogen separated by ca 20 30 my the 913 2 ma metamorphic episode appears to date a heating event restricted to the outermost edge of the western gneiss region leucosome formation in high grade gneisses geographically close to the jotun anorthosite is dated at 892 4 ma and suggested to reflect co2 rich fluid flux along shear zones