derivation of the 1 0 0 9 ga ferro potassic a type granitoids of southern norway by extreme differentiation from basic magmas major and trace elements sr and nd isotopic data as well as mineral compositions are presented for a selection of the 1 0 0 9 ferro potassic a type granitoids bessefjellet rustfjellet verhuskjerringi valle holum svofjell handeland tveit aseral lyngdal gabbronorites that occur close to the mandal ustaoset line mul of southern norway these hornblende biotite granitoids hbg define an extensive differentiation trend ranging from gabbronorites 50 wt sio 2 to granites 77 wt sio2 this trend is interpreted as resulting from extreme fractional crystallization of several basaltic magma batches with similar major and trace elements compositions at 930 ma the hbg suite displays a narrower range in isr 0 7027 0 7056 than in end t 1 97 down to 4 90 suggesting some assimilation of a rb depleted lower crust afc process or and source variability an age of 929 47 ma is given by a rb sr isochron on the holum granite sri 0 7046 0 0006 mswd 1 7 geothermobarometers indicate a low pressure of emplacement 1 3 2 7 kbar and an oxygen fugacity close to nno high liquidus temperatures are given by the apatite saturation thermometer 1005 1054 c and are in agreement with results from other studies the basaltic parent magmas of the hbg suite are partial melts of an hydrous mafic potassic source lying either in the lithospheric upper mantle or in the mafic lower crust derived from it this contrasts with the 930 ma anorthosite mangerite charnockite suite amc suite of the rogaland province for which a depleted lower crustal anhydrous gabbronoritic source has been indicated the present data imply the penecontemporaneous melting of two contrasting sources in southern norway the source duality could result from an increasing degree of metamorphism amphibolite to granulite from east to west an horizontal stratification of the lower crust or from the stratification of the lithosphere melting of the lower crust or upper mantle it may also indicate that the amc and hbg suites formed in two distinct crustal segments the linear alignment of the hbg suite along the mandal ustaoset shear zone suggests that a linear uprise of the asthenosphere following a lithospheric delamination under this structure could be the vector of the mantle heat 2003 elsevier science b v all rights reserved

eddies and the annular modes of climate variability the dominant modes of month to month varia tion in the troposphere are realistically simulated in a gen eral circulation model whose lower boundary is prescribed with realistic topography and seasonally varying climato logical sea surface temperatures in both hemispheres these internal modes describe a nearly zonally symmetric north south shifting of the zonal jets as anomalous westerlies vac illate between high 50 60 a nd low 30 40 latitudes the eddy structures evolve with the jets and the corre sponding eddy momentum forcings support the shifts in jet position stationary synoptic wave variations mainly ac count for the total eddy forcings in the northern south ern hemisphere pronounced eddy variations occur over the north atlantic sector

isotopic constraints on the genesis of the rogaland anorthositic suite southwest norway demaiffe d weis d michot j and duchesne j c 1986 isotopic constraints on the genesis of the rogaland anorthositic suite southwest norway in s deutsch and a w hofmann editors isotopes in geology picciotto volume chem geol 57 167 179 isotopic data were obtained on the sveconorwegian 1200 900 ma anorthosites and associated norites and charnockites of the rogaland igneous complex sw norway the isotopic data isr 0 703 0 7077 end 0 4 to 5 5 suf 4pb 1 8 1 8 2 so 5 2 to 6 6 c suggest an upper mantle origin for the parental magma of the anorthosites and related norites and jotunites or an origin in the lower crust by melting of mantle derived basic rocks shortly after their formation in two well documented cases the egersund ogna and the hidra bodies a progressive contamination by u depleted but not rb depleted lower crustal material is apparent during the differentiation process the late stage liquids have higher i up to 0 7086 lower but still slightly positive end less radiogenic pb isotopic composition the intrusive acidic rocks some of them of the charnockitic type display variable isotopic data is 0 7055 0 709 end 0 5 to 0 8 pb isotopic compositions comparable to that of some of the surrounding gneisses suggesting that there are in general no direct cogenetic relations between the anorthosites and the charnockites our data point to an origin of some of these acidic rocks by anatectic melting of the surrounding high grade metamorphic gneisses

petrology and geochemistry of the lyngdal granodiorite southern norway and the role of fractional crystallisation in the genesis of proterozoic ferro potassic a type granites abstract in south western norway the sveconorwegian orogenic thickening 1024 970 ma is followed by an important post collisional magmatism 950 930 ma divided in two suites vander auwera et al 2003 the anorthosite mangerite charnockite suite amc suite and the hornblende biotite granitoids suite hbg suite the hbg suite displays a continuous trend from gabbronorites to granites this paper presents the petrography and geochemistry major and trace elements sr nd isotopes of the lyngdal granodiorite and associated massifs tranevag and red granite massifs which belong to the hbg suite although being very close to the anorthosite massifs mafic microgranular enclaves mme resulting from magma mingling can be abundant and probably correspond to the parent magma of the studied plutons the lyngdal granodiorite and associated massifs are subalkaline metaluminous a type granitoids with high feo t feo t mgo ratio and k 2 o content forming a ferro potassic a type continuous trend from quartz monzodiorite to granite 56 72 wt sio 2 in harker diagrams the lyngdal tranevag plutons share the proterozoic rapakivi granites trend that they extend to lower sio 2 content major and trace element modelling as well as sr nd isotopes show that fractional crystallisation without assimilation is the differentiation process for lyngdal tranevag fractionating minerals are clinopyroxene hornblende plagioclase oxides biotite apatite zircon and allanite the red granite 71 75 wt sio 2 does not belong to this trend probably due to a different initial magma composition this study shows that ferro potassic a type granitoids can be derived by fractional crystallisation from mafic magmas

sveconorwegian massif type anorthosites and related granitoids result from post collisional melting of a continental arc root article i nfo two magmatic suites were emplaced during the post collisional evolution of the sveconorwegian orogeny an anorthosite mangerite charnockite suite amc suite and an hornblende and biotite bearing granitoids suite hbg suite the amc suite is exclusively located in the westernmost and warmest part of the orogen in granulite facies gneisses whereas the hbg suite intruded in the rest of the orogen but not in the granulite domain new u pb zircon geochronological data confirm previous age determinations 970 932 ma hbg suite and 933 916 ma amc suite the mafic facies of the two post collisional magmatic suites have similar geochemical compositions but the hbg differentiation trend displays higher cao sr u and th as well as lower k2o and feot mgo than the amc differentiation trend the hbg suite is hydrous and has a broadly higher fo2 whereas the amc suite is anhydrous the inferred parent magmas of both suites have overlapping initial sr nd and pb isotopic compositions with increasing differentiation the two trends point towards two different crustal contaminants together with the recent recognition of a major crustal shear zone located just east of the amc suite this difference suggests that the suites were emplaced in two different lithotectonic units using published experimental constraints and geochemical modeling we suggest that the mafic facies of both suites were produced by partial melting of lower crustal sources which were previously underplated probably during the evolution of a long lasting convergent margin later these lower crustal sources were modified by the regional granulite facies metamorphism 1 035 to 0 97 ga prevailing in the westernmost part of the orogen thus producing an anhydrous lower crustal source for the amc suite accordingly we conclude that the sveconorwegian massif type anorthosites result from partial melting of the continental arc root this process if accepted for other amcg anorthosite mangerite charnockite granite complexes was possible in the proterozoic because of a sufficiently high temperature but not in the archean because in subduction zones the main transfer to the crust was then felsic tonalites granodiorites and not basaltic we thus further suggest that the onset of massif type anorthosites at the beginning of the proterozoic may mark the time when plate tectonics began to operate in a similar way as today

an upper limit to ground deformation in the island of tenerife canary islands for the period 1997 2006 continuous monitoring of ground deformation in the volcanic island of tenerife canary islands is based on gps networks since there are as yet no tiltmeter stations installed on the island however there is a world class astronomical observatory on the island the el teide observatory where four tiltmeters two aligned in the north south and the other two in the east west are monitoring the movements of the solar telescope themis themis heliographic telescope for the study of solar magnetism and instabilites is among the three largest solar telescopes in the world since themis is located a few kilometers from the main volcanic structures of the island in particular the el teide pico viejo stratovolcano and the precision of the inclinometers is comparable to those used in geophysical studies we carried out the analysis of the tilt measurements for the period 1997 2006 the tiltmeters at themis are placed in the seventh floor of a tower hence their sensitivity to geological processes is reduced compared to geophysical installations however themis measurements are the only terrestrial data available in tenerife for such a long period of observations which include the sustained increase in seismic activity that started in 2001 in this sense a significant change was found in the east west tilt of approximately 35 radians between the years 2000 and 2002 some theoretical models were calculated and it was concluded that such tilt variation could not be due to dike intrusions nor a volcanic reactivation below the el teide pico viejo volcano the most likely explanation comes from dislocations produced by a secondary fault associated to a major submarine fault off the eastern coast of tenerife in any case taking into account the nearly permanent data recording at themis they could be considered as a complement for any ground deformation monitoring system in the island

whither arctic climate large changes in arctic climate have been observed in his perspective shindell 1 shows that models have difficulty reproducing these changes raising doubt over their ability to elucidate the causes of the observed changes or predict future trends he argues that these difficulties can largely be attributed to gravity waves which are not yet well represented in the models these waves are generated by atmospheric disturbances such as storm fronts strong wind shears and flow over mountains and play a key role in many of the observed changes 1 http www sciencemag org cgi content full 299 5604 215

a mechanistic model of the northern annular mode 1 the northern annular mode nam is the leading mode of variability in the northern hemisphere the nam consists of a meridional dipole of the zonal mean zonal wind that extends into the stratosphere during the winter season during the high index state of the nam high latitude westerly winds are stronger than normal leading to a stronger and colder polar vortex over the past few decades observations show a trend toward higher nam index values to investigate whether this trend is a result of natural variability or is related to greenhouse warming a mechanistic model is developed that provides a simple analogue of the nam the model represents the interaction between the zonally symmetric flow and planetary waves for two meridional modes of variation greenhouse warming is specified in the model by varying the radiative equilibrium meridional temperature gradient variations in the second meridional mode qualitatively resemble those of the observed nam model runs that correspond to larger greenhouse gas concentrations yield on average higher nam index values

on the nonlinear versus linearized lower boundary conditions for topographically forced stationary long waves abstract for quasi geostrophic stationary long waves forced by topography the nonlinear lower boundary condition is derived in terms of the geopotential height and compared with the linearized version the common practice of replacing terms describing the flow over and around a mountain by upstream zonal flow over the mountain and evaluating the resulting condition at sea level is found to be a good approximation for the cases considered and does not need to be modified as sometimes suggested specifically it is found that this approximation does not affect for most cases the lower boundary condition expressed in terms of the geopotential height provided that the stationary wave is not near resonance at resonance the eddy advection terms may become important for large amplitude waves when dissipation and surface diabatic heating are taken into account

reply to comment on dykes faults and paleostresses in the teno and anaga massifs of tenerife canary islands by j a rodriguez losada and a hernandez pacheco abstract we welcome the comment by rodriguez losada and hernandez pacheco hereafter lp and we are pleased that they have no objections to the conclusions of marinoni and gudmundsson 2000 hereafter mg the lp comment deals only with the anaga massif and mostly with 1 dykes supposed to be folded by post emplacement ductile deformation 2 tilting of the oldest part of the anaga succession 3 selection of profiles 4 the horizontal extension due to dykes and 5 the paleostress field of anaga we reply briefly to these points below

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

wave driven zonal flow vacillation in the southern hemisphere the variability of the zonal mean flow in the southern hemisphere during the period 1985 94 is studied using european centre for medium range forecasts analyses the dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608s this structure is dominant in all seasons and has similar variance in all seasons the temporal variance of the amplitude of this mode is well modeled as gaussian red noise with a correlation e folding time of about 10 days zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations the eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward

features of crustal structure under the canary islands abstract the data and interpretation of a seismic refraction project carried out in the canary islands in 1977 and 1979 are presented the moho is reached at about 15 km under fuerteventura gran canaria and tenerife whereas under lanzarote a value of 11 km has been found the velocity at the surface varies even within one island from 2 8 to 4 4 km s there are variations in the velocity of the main crustal layer under the volcanic deposits a continuous velocity depth function seems to be more appropriate for the island of tenerife contrary to fuerteventura lanzarote and gran canaria which seem to have a layered structure there is evidence for pronounced structural differences between lanzarote and fuerteventura the mantle velocity has a value of about 8 0 km s under the western islands whereas a very low value of 7 4 km s has been found under lanzarote and fuerteventura despite the clear structural differences between the islands our results leave little doubt about the oceanic character of all the islands the differences between the eastern and western group may be due to the islands being situated close to the african continental margin the seismic velocities under the volcanic deposits do not support the idea of a common basement for all the islands they rather suggest independent volcanic edifices finally a comparison of the structure of the crust under the canary islands with that under other volcanic islands reveals remarkable similarities

phase equilibria of the lyngdal granodiorite norway implications for the origin of metaluminous ferroan granitoids the proterozoic 950 ma lyngdal granodiorite of southern norway belongs to a series of hornblende biotite metaluminous ferroan granitoids hbg suite coeval with the post collisional rogaland anorthosite mangerite charnockite amc suite this granitoid massif shares many geochemical characteristics with rapakivi granitoids yet granodiorites dominate over granites to constrain both crystallization p t fo2 h 2o in melt and magma generation conditions we performed crystallization experiments on two samples of the lyngdal granodiorite with 60 and 65 wt sio2 at 4 2 kbar mainly at fo2 of nno nickel nickel oxide to nno 1 and under fluid saturated conditions with various h2o co2 ratios for each temperature comparison between experimental phase equilibria and the mineral assemblage in the lyngdal granodiorite indicates that it crystallized between 4 and 2 kbar from a magma with 5 6 wt h2 oa t an fo2 of nno to nno 1 these oxidized and wet conditions sharply contrast with the dry and reduced conditions inferred for the petrogenesis of the amc suite and many other rapakivi granites worldwide the high liquidus temperature and h2o content of the lyngdal granodiorite imply that it is not a primary magma produced by the partial melting of the crust but is derived by the fractionation of a mafic magma lyngdal type magmas appear to have volcanic equivalents in the geological record in particular our results show that oxidized high silica rhyolites such as the bishop tuff could be derived via fractionation of oxidized intermediate magmas and do not necessarily represent primary crustal melts this study underlines the great variability of crystallization conditions from anhydrous to hydrous and reduced to oxidized and petrogenetic processes among the metaluminous ferroan magmas of intermediate compositions granodiorites quartz mangerites quartz latites suggesting that there is not a single model to explain these rocks

dynamic winter climate response to large tropical volcanic eruptions since 1600 1 we have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy based reconstructions and modern instrumental records of cold season surface air temperature warm anomalies occur throughout northern eurasia while cool anomalies cover northern africa and the middle east extending all the way to china in north america the northern portion of the continent cools with the anomalies extending out over the labrador sea and southern greenland the analyses confirm that for two years following eruptions the anomalies strongly resemble the arctic oscillation northern annular mode ao nam or the north atlantic oscillation nao in the atlantic eurasian sector with our four century record the mean response is statistically significant at the 95 confidence level over much of the northern hemisphere land area however the standard deviation of the response is larger than the mean signal nearly everywhere indicating that the anomaly following a single eruption is unlikely to be representative of the mean both the mean response and the variability can be successfully reproduced in general circulation model simulations driven by the solar heating induced by the stratospheric aerosols these models produce enhanced westerlies from the lower stratosphere down to the surface the climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the ao nam or nao

the statistical connection between tropospheric and stratospheric circulation of the northern hemisphere in winter abstract the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the northern hemisphere are determined applying the canonical correlation analysis with this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions the one dataset is the 50 hpa geopotential height field the other set consists of different height fields of the tropospheric pressure levels 200 500 700 and 850 hpa and the temperature of the 850 hpa pressure level for the winter months december january february two natural coupled modes a barotropic and a baroclinic one of linear relationship between stratospheric and tropospheric circulation are found the baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the north atlantic the corresponding temperature

genetic implications of pb isotopic geochemistry in the rogaland anorthositic complex southwest norway abstract 110 samples from different massifs of the rogaland igneous complex have been analyzed for whole rock pb isotopic compositions these data show no evidence of rocks older than 1500 ma this is probably the time of extraction of the magmatic precursors from the mantle the pb data indicate a mantle origin for the parental magmas of the massiftype anorthosites and of the jotunitic series nevertheless an origin by partial melting of mantle derived basic material in the lower crust cannot be excluded especially for the latter the charnockitic rocks associated with the anorthosites could either be anatectic melts of the enclosing gneisses or residual liquids of anorthosite differentiation contaminated by slightly u depleted lower crustal material although in some cases upper crustal material has also contributed to the contamination

propagation of planetary waves between the troposphere and stratosphere abstract the propagation of planetary waves between the troposphere and stratosphere is investigated using a linear time dependent primitive equation model it is found that the tropopause acts like a valve for the propagation of planetary waves the key parameters controlling the valve are the vertical gradient of buoyancy frequency and the vertical shear of the zonal winds at the tropopause for a given wind profile smaller gradient of buoyancy frequency enhances the propagation of planetary waves for a given profile of buoyancy frequency the larger the shear the more the wave activity is trapped in the troposphere and therefore there is less left to propagate into the stratosphere the transmission across the tropopause is however not sensitive to zonal winds in the upper stratosphere the propagation of planetary waves is very sensitive to transience more transient waves propagate more vertically within the troposphere and for more transient waves more wave activity is transferred into the

geochemistry of the lyngdal hyperites s w norway comparison with the monzonorites associated with the rogaland anorthosite complex the lyngdal hyperites lyhy crop out as two small post tectonic intrusions of gabbro noritic to monzonoritic composition at the extreme south of norway they display subophitic textures with plagioclase laths an40 to an58 orthopyroxene en56 to en62 clinopyroxene wo47 5en39fs13 5 ilmenite magnetite and interstitial myrmekite fringes k feldspar quartz apatite and biotite the sio2 content is very constant 50 53 but k2o ranges from 1 to 1 6 in differentiated facies ree patterns are smooth layb n 6 the hyperites define an rbsr isochron of 910 82 ma 2 with an initial ratio of 0 7054 nd is slightly positive 0 to 2 and average lead isotopic initial ratios are 17 45 206pb204pb i and 15 51 207pb204pb i the lyhy represent magmatic liquids that have not fractionated large amounts of plagioclase they are quite comparable to the rocks of the monzonoritic series that occur in the nearby rogaland anorthosite complex 1 the plagioclases have the same composition plagioclase phenocrysts are locally present 2 they display enrichments in tio2 p2o5 and k2o 3 they have comparable ree patterns 4 the isotopic data show that the monzonorites and the lyhy derive from the same isotopic reservoir the lyhy nevertheless differ from the monzonorites by their high al content al2o3 18 5 and their lower feotot content feototfeotot mgo 0 62 the geochemical and isotopic diversity of the monzonoritic magmatism including the lyhy implies that each occurrence represents a distinct magma batch generated from a distinct source the lyhy could tentatively be interpreted as a fe poor mg rich end member of the monzonoritic magmatism occurring to the east of the anorthosite complex

a mechanistic model study of slowly propagating coupled stratosphere troposphere variability observational studies reveal the oscillatory nature of coupled stratosphere troposphere variability which is characterized by a slowly downward propagating anomalous zonal mean zonal wind during the winter the term slowly is employed compared to the rapid variation associated with stratospheric sudden warmings in fact strong stratospheric warming events are embedded in this slowly propagating variability as is shown in a companion paper kodera et al this issue in the present study the mechanism producing such variability at all levels of the atmosphere is investigated by developing a simple model that extends from the earth s surface to 80 km altitude the model is a quasi geostrophic channel model similar to that used by holton and mass 1976 but it includes two meridional fourier components and latitudinal variation in the gradient of the coriolis parameter by this extension the present model can incorporate both the subtropical and polar night jet and also treat the horizontal propagation of planetary waves as well as vertical propagation the results of the simulation reproduce qualitatively well the main observed features interaction between the planetary waves and zonal mean flow produces oscillations in the winter stratosphere and zonal wind anomalies created in the subtropics of the stratopause propagate downward into the polar region of the troposphere which provoke changes in the meridional propagation of tropospheric planetary waves

dynamics of volcanic systems in iceland example of tectonism and volcanism at juxtaposed hot spot and mid ocean ridge systems volcanic systems are swarms of tectonic fractures and basalt volcanoes formed as a result of plate pull as the plates are pulled apart associated with the mid ocean ridges and the magma dynamics of the iceland mantle plume most systems are 40 150 km long 5 20 km wide and develop a central volcano they supply magma to all eruptions in iceland data obtained in the last few years have greatly improved our knowledge of their volcanotectonic environment as a result the geometry of the plume is better constrained and the crust previously considered thin 10 km is now modeled as thick 20 40 km depending on the location of the volcanic systems their activity either decreases or increases faulting in the two main seismic zones from this we can infer that emplacement of the feeder dike to the largest historical eruption in iceland that of laki in 1783 increased shear stress in the south iceland seismic zone and almost certainly triggered the largest m 7 1 in 1784 historical earthquake in ic

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

detection of displacements on tenerife island canaries using radar interferometry tenerife is one of the most well monitored islands of the canaries but the surveillance generally is centred on las canadas caldera where the teide volcano is located in the last 180 000 yr the eruptions on tenerife island have never occurred in the same volcanic structure except for the teide and pico viejo central volcanic system so that a complete monitoring network would have to cover the whole island as a result synthetic aperture radar interferometry insar is being used on tenerife because this space technique can provide a displacement map of the surface of the earth with centimetre precision this paper presents the results obtained on tenerife island using 18 sar images acquired by the ers 1 and ers 2 satellites during the period 1992 2000 two important results have been obtained no deformation on las canadas caldera coinciding with results obtained using terrestrial techniques and two subsidence episodes outside monitoring areas in the nw of the island in the region of the last historic eruptions these results show that insar is a useful technique for monitoring the entire island thus allowing us to discover deformations in areas that are not routinely or easily monitored this technique has been used in combination with global positioning system gps observation of a global network on the island to define a new geodetic monitoring system the possible causes of the deformations observed have been studied in an endeavour to discern if they might be of natural origin in particular linked to a reactivation of prior volcanic activity examination of the geophysical observations on the island human activities underway and the results of the modelling seem to indicate that at least part of the deformations may be caused by changes in the groundwater level and therefore are not linked to a volcanic reactivation this result is important because it implies that if geodetic volcano monitoring is to be performed on the island the system used must be capable of discerning between various possible origins of the deformation by analysing their patterns and ancillary information from other sources in this regard insar is a basic tool on account of its unpaired wide area coverage and spatial density

petrogenesis of monzonoritic dykes in the egersund ogna anorthosite rogaland s w norway trace elements and isotopic sr pb constraints two major monzonoritic dykes occur in the egersund ogna anorthositic massif s w norway the lomland dyke which varies from norite to monzonite and the vettaland ferronoritic dyke they are characterized by high fe ti and p contents low sio2 variable k2o 0 5 4 5 and high fe mg ratios small variations in ree distribution are observed inside the lomland dyke la yb 12 lree ca 150 180 chondrite normalized values neutral to slightly positive eu anomaly part of the vettaland dyke is severely depleted in zr rb and ree and shows a positive eu anomaly all rocks are depleted in u and th and show very low cr and ni contents as well as high sr contents 400 600 ppm variation within the lomland dyke is satisfactorily ex plained through subtraction of an apatite bearing noritic cumulate the role of apatite is predominant in controlling the ree behaviour eutectic partial melting of a fe rich noritic cumulate containing apatite under low ph2o conditions is suggested for the vettaland dyke by ree modelling sr isotopic initial ratios are different in lomland ca 0 708 and vettaland ca 0 706 dykes these values preclude direct derivation from the mantle as well as comagmatic relationship with anorthosite contamination of a mantle derived magma by deep crustal material or anatexis of the lil depleted lower crust is compatible with the low u and th contents and with the pb isotopic ratios the vettaland partial melting process is extended to all monzonoritic types the necessary heat being provided by the high temperature anorthositic crystal mush

crystallization of apatite in natural magmas under high pressure hydrous conditions with particular reference to orogenic rock series two separate series of hydrous experiments involving 1 imposing apatite saturation on a series of igneous rock compositions from basanite to rhyolite and 2 crystallizing similar natural rock compositions progressively until apatite appears demonstrate a close dependence between apatite saturation and silica content of the magma and determine p2o5 levels at a given silica value and temperature at which that composition may be expected to crystallize apatite the effect of pressure on apatite solubility is not great and is most significant for silicic compositions

dykes faults and palaeostresses in the teno and anaga massifs of tenerife canary islands abstract a structural field study was made of 578 sheet intrusions mostly dykes and 153 mostly normal faults dissecting the anaga and teno massifs where a complex volcanic succession of tertiary age the old basaltic series representing the shield building stage of tenerife canary islands crops out many of the intrusions mostly sub vertical mafic dykes are emplaced by multiple magma injections with cumulative thicknesses mostly less than 2 m dyke tips are exposed and preserved for 12 of the dykes three differently oriented sets of dykes exist in the anaga massif nnw sse nne ssw e w whereas there is only one main set in teno trending nnw sse dyke swarms and other structural features having similar orientations also exist in other canary islands a minimum value of the horizontal component of extension induced by dykes is computed using a step of 5 of azimuth accounting also for the dip of dykes the cumulative crustal dilation is at least 300 m 4 in anaga and 270 m 6 in teno the maximum extension peaks at n75 in anaga and n60 in teno indicating a general prevailing extension in direction ene wsw most of the measured faults are normal and strike nnw sse computation of palaeostresses from inversion of fault slip data sets suggests the existence of a polyphase brittle deformation due to an extensional stress field with the minimum compressive principal axes trending ne sw and wnw ese

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

the effect of pressure on dsr plag melt and dcr opx melt implications for anorthosite petrogenesis the crystal liquid partition coefficients for sr and cr dsr and dcr have been determined from electron microprobe analyses of plagioclase liquid and orthopyroxene liquid pairs produced in melting experiments run at pressures from 1 bar to 27 kbar on two compositions relevant to anorthosite petrogenesis one is a primitive jotunite hypersthene monzodiorite tj the other is a sample of an anorthositic dyke 500b results indicate that dsr plag liq remains nearly constant with increasing pressure tj 1 7 to 2 6 500b 0 9 to 1 4 this modest variation apparently results from the combined and opposing effects of crystal chemistry and pressure dsr increases with the albite content of plagioclase which itself increases with pressure along a composition s liquidus so pressure must have an intrinsic negative effect the two models for dsr j blundy b wood geochim cosmochim acta 55 1991 193 209 i bindeman a davis m drake geochim cosmochim acta 62 1998 1175 1193 that take into account the strong correlation between dsr and plagioclase composition overestimate dsr at high pressure whereas the two models that ignore plagioclase composition s morse geochim cosmochim acta 56 1992 1735 1738 r nielsen comput geosci 18 1992 773 788 underestimate it moreover since none of these models takes into account any pressure effect the discrepancies between predicted and observed dsr increase with pressure for all models the new results also show that dcr opx liq increases significantly with pressure dcr 2 at 1 atm and 14 2 at 10 kbar these new data confirm earlier less precise determinations of dcr that were used to infer a high pressure origin for al and cr rich orthopyroxene megacrysts the calculated sr and cr concentrations of liquids in equilibrium at 10 kbar with plagioclase and orthopyroxene megacrysts from anorthosite massifs sr 370 to 610 ppm and cr 20 to 130 ppm are in the range of what is observed in high al gabbros and primitive jotunites the inferred parent magmas of massive anorthosites fl 2000 published by elsevier science b v all rights reserved

pb isotope geochemistry of a massif type anorthositic charnockitic body the hidra massif rogaland s w norway abstract the hidra massif rogaland complex s w norway is a massif type anorthositic charnockitic body it consists of undeformed anorthosites and leuconorites grading into fine grained jotunites at the contact with the granulite facies gneisses of the metamorphic envelope a stockwork of charnockitic dykes cross cuts the massif the pb isotopic compositions of the anorthosites and leuconorites are comparable or slightly less radiogenic than those of the jotunites 206 pb 204 pb from 18 079 to 19 307 207 pb 204 pb from 15 568 to 15 657 and 208 pb 204 pb from 37 617 to 38 493 these values are compatible with an upper mantle origin for the parental magma of jotunitic composition and for the plagioclasic cumulates but show the incorporation of lower crustal material u depleted and thus less radiogenic the charnockitic dykes have significantly less radiogenic pb isotopic compositions 206 pb 204 pb from 17 472 to 19 171 207 pb 204 pb from 15 489 to 15 620and 208 pb 204 pb from 36 991 to 40 922 which can be explained by a larger proportion of lower crustal contamination material the contaminant could be the granulite facies gneisses of the metamorphic envelope this interpretation is compatible with the k rb relationships of these rocks and with the o and sr isotopic geochemistry the proportion of contaminating lead in the charnockitic dykes can be estimated at 55 15 considering the border facies jotunite as the uncontaminated parental magma and the least radiogenic gneiss of the metamorphic envelope as the contaminant

some phase equilibrium constraints on the origin of proterozoic massif anorthosites and related rocks experimental data in the range of 1 bar to 13 kbar enable us to introduction map the liquidus equilibria relevant to proterozoic massif anorthere is hardly a consensus on the petrogenesis of thosites and related mafic rocks massif anorthosites are widely proterozoic massif anorthosites but many investigators believed to have formed by accumulation of plagioclase into highbelieve in a petrogenetic scheme that involves at least al basaltic liquids mantle derived basaltic liquids fractionating two major stages 1 extensive crystallization asat pressures sufficiently high 10 13 kbar to crystallize the highly similation of a mantle derived magma ponded at or aluminous orthopyroxene megacrysts typically observed in anorthosite near the base of the crust that produces suspensions of massifs reach plagioclase saturation at low normative silica contents plagioclase in fe rich high al gabbroic liquids followed peritectic like equilibria e g liq opx plag cpx sp by 2 intrusion of these suspensions into the mid upper and a thermal divide on the plagioclase pyroxene liquidus surface crust where they form complex magma chambers e g ensure that mantle derived liquids become nepheline normative with duchesne 1984 emslie 1985 ashwal 1993 wiebe further crystallization and crustal assimilation at depth such 1994 a key component of the scheme is the presence liquids cannot produce the full range of troctolitic noritic to trocin most massifs of high al orthopyroxene megacrysts tolitic gabbroic mineral assemblages observed in anorthosite massifs haom emslie 1975 that appear to preserve a record without extensive low pressure granite assimilation conversely the of the high pressure stage maquil duchesne 1984 array of plausible anorthosite parental liquids not only lies along longhi et al 1993 the structures of massifs vary from the trace of the plagioclase two pyroxene cotectic from 10 to 13 those that are composites of multiple diapiric intrusions kbar but also straddles the thermal divide on the plagioclase harp lake emslie 1980 rogaland duchesne 1984 pyroxene liquidus surface this condition requires mafic source to intrusive bodies with well developed layering of regions such as lower continental crust or foundered mafic plutons leucocratic troctolites and leuconorites or leucogabbros for liquids parental to massif anorthosites and associated mafic overlain by masses of anorthosite michikamau emslie intrusions 1970 laramie frost et al 1993 so there may be

genesis of intermediate igneous rocks at the end of the sveconorwegian grenvillian orogeny s norway and their contribution to intracrustal differentiation abundant ferroan metaluminous granitoids 970 950 ma emplaced at the end of the sveconorwegian collisional orogeny 1130 900 ma are dominated by intermediate to silicic compositions with rare mafic facies both 73 fractional crystallization of an amphibole bearing gabbroic cumulate substracted from the parent mafic composition and 30 non modal batch melting of an amphibolitic source equivalent in composition to the mafic facies produce a monzodioritic liquid with appropriate trace element composition a better fit is obtained for the partial melting process both processes could have occurred simultaneously to produce mafic cumulates and restites as there is no evidence for large volumes of dense mafic rocks in the sveconorwegian upper crust these dense mafic rocks were probably produced in the lower crust formation of these granitoids thus contributed to the vertical stratification of the proterozoic continental crust and also to the transfer of water from the lower crust to the surface

wave maintained annular modes of climate variability abstract the leading modes of month to month variability in the northern and southern hemispheres are examined by comparing a 100 yr run of the geophysical fluid dynamics laboratory gcm with the ncep ncar reanalyses of observations the model simulation is a control experiment in which the ssts are fixed to the climatological annual cycle without any interannual variability the leading modes contain a strong zonally symmetric or annular component that describes an expansion and contraction of the polar vortex as the midlatitude jet shifts equatorward and poleward this fluctuation is strongest during the winter months the structure and amplitude of the simulated modes are very similar to those derived from observations indicating that these modes arise from the internal dynamics of the atmosphere dynamical diagnosis of both observations and model simulation indicates that variations in the zonally symmetric flow associated with the annular modes are forced by eddy fluxes in the free troposphere while

crustal extension from exposed sheet intrusions review and method proposal abstract sheet intrusions are probably the most widespread magmatic features on earth they create a space for themselves by dilating the host rock the exposed sheet intrusions allow an estimate of a minimum value of the extension to which the crustal layers and the volcanic edifices are subject the correct evaluation of the contribution of sheet intrusions to the crustal extension is of great importance in various geologic settings the current methods used to evaluate the extension due to exposed sheet intrusions are reviewed in this paper the effect of the dip of sheet intrusions on the evaluation of horizontal crustal extension is analysed if the dip effect is neglected and the intrusions are sub vertical the error due to the dip effect in the extension evaluation is small if the intrusions are shallow dipping the error may be great and varies as a function of the dyke dip for dykes with dip range 45 65 the error due to neglecting the dip effect is 30 to 15 increasing discrepancies of more than 25 are produced on the computed dilation when the intrusions progressively dip less than 50 a simple method based on structural field measurements of exposed sheet intrusions and on trigonometric considerations is presented as an improvement of pre existing methods to estimate the horizontal component of the crustal extension using this method field data of 1154 dykes from different geodynamic contexts are analysed the horizontal component of extension is computed using dyke data from the tertiary massifs of lanzarote and tenerife and from the active stratovolcanoes of monte somma vesuvius and etna since the analysed dykes are steeply dipping the cumulative difference between the extension computed neglecting and taking into account the dip effect remains less than 10 for all the data sets the percentage difference is nearly constant and cumulatively higher for monte somma where the mean dip of the intrusions is smaller in lanzarote 237 dykes emplaced between 15 5 and 3 7 ma give a peak extension of 276 m in direction n135 and a time averaged minimum extension rate of 1 9 10 2 to 2 3 10 2 mm a 1 in tenerife an extension of 562 m is computed in the direction n65 from 563 dykes emplaced from 7 4 to 3 3 ma the time averaged minimum rate of extension for the tertiary massifs of tenerife ranges from 0 14 to 0 25 mm a 1 the peak extension computed for monte somma is 81 7 m in the direction n90 based on 96 exposed sheets very likely most of monte somma sheets intruded within 12 ka giving a time averaged minimum extension rate of 7 mm a 1 from 184 exposed dykes of etna a minimum extension rate of 6 2 mm a 1 is computed peak extension is 212 m in direction n35 the poor resolution of age constraints may affect deeply the reliability of the extension rates however from the examples presented it appears that the extension rates of pre erosional successions from intraplate volcanic islands can be smaller than those of active stratovolcanoes this may suggest a more active dynamics in the stratovolcanoes

effects of canary hotspot volcanism on structure of oceanic crust off morocco analysis of over 6400 km of multichannel seismics mcs and 50 sonobuoy reflection and refraction experiments reduced both in the domain of x t and tau p shows that a region within the jurassic quiet zone off morocco underwent dramatic changes as a result of the passage of the lithosphere over the canary hotspot commencing approximately 60 ma a seismic unit ucf interpreted as volcanic in origin is observed within the sediments in a region characterized by a broad bathymetric swell it shows diffractions from its upper surface and an internally chaotic seismic facies and pinches out between sedimentary units of continuous subparallel facies a velocity inversion is noted between the ucf 4 7km s and the underlying sediment 3 1 km s the ucf is time transgressive it lies near the cretaceous s tertiary boundary in the northern portion of the study area and is younger to the south kinematic studies of the movement of the canary hotspot relative to africa show that the hotspot first appeared off nw africa about 60 ma and was located beneath oceanic crust in the region where the ucf is observed depth to basement measurements in areas not effected by the hotspot show a consistent linear trend of increased depth with age in areas effected by the hotspot the thermal rejuvenation is evident as basement depths shoal with increased proximity to the present hotspot the reheating of the crust resets the thermal age of the lithosphere with many of the properties of crust of a younger age subsidence curves of the reheated crust off morocco show good correlation to subsidence curves of other reheated crust on a global basis a zone characterized by high crustal velocities 7 1 7 4 km s and greater crustal thicknesses by 1 2 km is observed in an area that corresponds to the bathymetric swell the region of the ucf and the reelevated basement the high velocities and increased crustal thickness are interpreted to be the result of underplating and assimilation of existing oceanic crust caused by the canary thermal anomaly the presence of high crustal velocities coupled with a thickened crustal section has been noted on various passive margins of the world they have generally been attributed to the thermal processes associated with continental rifting off morocco we believe that similar thermally induced phenomena have occurred but that here the heat anomaly was the midplate volcanism associated with the canary hotspot

commingling of magmas in the bjerkrem sogndal lopolith southwest norway evidence for the compositions of residual liquids a detailed re examination of some of the more fractionated portions of the bjerkrem sogndal lopolith bsl has provided evidence for widespread mixing between quartz mangeritic and monzonoritic eia rekefjord magmas the higher temperature monzonoritic liquids are preserved as chilled pillows within quartz mangerite chemical compositions of these and other fine grained monzonorites suggest that they are chilled residual liquids related to the bsl and that they were in equilibrium with the more fractionated cumulates of the bsl the chilled monzonoritic liquids appear to define a fractionation trend of increasing sio2 up to 60 wt the quartz mangerites appear to represent separate partial melts derived from the country rock

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 norite mangerite relationships in the bjerkreim sokndal layered lopolith southwest norway the transition zone between the anorthositic noritic rhythmic units and the mangeritic unit of the bjerkreim sokndal layered lopolith southwest norway is characterized by thick layers of ultramafic rock uml interleaved with norites in the lower part and mangerites in the upper part in the latter rocks large mesoperthite crystals occur in a fine grained groundmass porphyritic texture rapid variations in chemical composition are shown by the mafic minerals especially by olivine fos0 to fo19 and by ti magnetite 10 19 tio the whole rock composition of the uml does not change in the upper part of the transition zone and the fe fe mg ratio of the mangerites remains constant bowen trend formation of the uml through liquid immiscibility is rejected because 1 the liquidus minerals are not always identical in the fe rich and associated silica rich rocks 2 the distribution of p205 ree and ba between associated rocks are not in agreement with experimental data 3 the major elements vary along parallel trends in the creigh diagram cumulative processes and adcumulus growth can best explain the uml oscillatory nucleation can account for the norites and flotation of mesoperthite is plausible in the mangerites where accumulation of feldspar is evidenced by a strong positive eu anomaly and porphyritic textures the mangeritic unit of the lopolith is interpreted as a flotation cumulate at the roof of the magma chamber the residual liquids of the bjerkreim sokndal differentiation were either trapped in the mangerites or expelled in the form of dykes or were mixed with quartz mangeritic liquids above the intrusion

infrastructure and mechanics of volcanic systems in iceland the divergent plate boundary in iceland consists of more than two dozen systems where most of the volcano tectonic activity takes place at the surface the volcanic systems are characterised by 5 20 km wide and 40 100 km long swarms of tension fractures 102 m long normal faults 103 m long and volcanic fissures the holocene fissure swarms are confined to less than 10 000 year old basaltic lava flows mostly pahoehoe occurring near the centre of the active rift zone in any particular swarm the number of tension fractures exceeds that of normal faults all tension fractures and normal faults are vertical at the surface indicating that the surface parts were generated by an absolute tension in addition to a fissure swarm many volcanic systems have a central volcano some of which have developed collapse calderas in the late tertiary and pleistocene lava pile of iceland extinct volcanic systems are represented by local sheet swarms and regional dyke swarms the sheet swarms are normally circular or slightly elliptical several kilometres in radius and are confined to the extinct central volcanoes many swarms are associated with large plutons exposed at 1 2 km depth beneath the initial top of the rift zone and presumably the uppermost parts of extinct crustal magma chambers and in short traverses up to 90 of the rock may consist of sheets the sheets have a very variable strike dip on average 45 65 mostly towards the centre of the associated volcano and have an average thickness of about 1 m the regional dykes occur outside central volcanoes in swarms that are commonly 50 km long and 5 10 km wide in several kilometre long traverses commonly 1 5 of the rock consist of dykes but occasionally as much as 15 28 most regional dykes are subparallel and subvertical the average dyke thickness in the pleistocene swarms is less than 2 m but 4 6 m in the tertiary swarms while active the volcanic systems in the rift zone are supplied with magma from reservoirs located at the depth of 8 12 km at the boundary between the crust and upper mantle the reservoirs are partially molten with totally molten top regions and of cross sectional areas similar to those of the volcanic systems that they feed some active volcanic systems especially those that develop central volcanoes high temperature areas and calderas have in addition to the deep seated magma reservoirs shallow crustal magma chambers located at 1 3 km depth which in turn are fed by the deeper magma reservoirs it is proposed that the regional dyke swarms are supplied with magma largely from the deep seated reservoirs whereas the local sheet swarms are mainly fed from the associated crustal magma chambers because the volume of a crustal chamber is less than that of its deeper source reservoir a single magma flow dyke intrusion from the reservoir may trigger tens of magma flows sheet intrusions from the chamber which is one explanation for the enormous number of sheets associated with many central volcanoes the sheets follow the stress trajectories of the local stress fields around the source chambers whereas the regional stress field associated with the divergent plate movements controls the emplacement of the regional dykes it is suggested that many dykes develop as self affine some as self similar structures when applied to the krafla volcanic system in northern iceland model calculations suggest that a magma flow from the krafla reservoir with regional dyke formation should occur on average once every several hundred years and that tens of sheets might be injected from the shallow krafla chamber and triggered by a single magma flow from the krafla reservoir these results are in broad agreement with the available data

rare earth element geochemistry and strontium isotopic composition of a massif type anorthositic charnockitic body the hidra massif rogaland sw norway abstract the hidra massif rogaland complex sw norway mainly consists of plagioclase cumulates anorthosites and leuconorites which grade progressively into a fine grained 200 m locally porphyritic jotunitic rock towards the contact with the granulite facies gneisses the massif is cross cut by thin 10 cm up to 1 m charnockitic dykes the petrographical and geochemical evolution of the hidra massif can be explained by fractional crystallization of a jotunitic parental magma major and trace element constraints indicate that mafic phases are underabundant in the exposed levels of the massif most likely as a result of plagioclase flotation in the early stages of solidification partitioning into the cumulate minerals mainly plagioclase and orthopyroxene governs the trace element contents of the leuconoritic adcumulates however the trace element geochemistry of the apparently early formed anorthositic orthocumulates largely depends upon the amount of a trapped intercumulus liquid on the basis of trace element abundances high ree rb th u negative eu anomalies the silicic charnockitic dykes can be considered as the residual liquid of the anorthositic fractionation trend the higher initial 87 sr 86 sr ratios 0 7086 0 0006 vs 0 7055 0 0004 for the plagioclase cumulates and jotunites point to contamination of the charnockitic liquids by surrounding gneissic material

tectonic evolution of the emergent part of a volcanic ocean island lanzarote canary islands abstract a reconstruction of the structural evolution of lanzarote confirms the existence of two principal stages of construction of the island separated by a main erosional event the first pre erosional is the shield stage miocene pliocene in age which is divided in three stratigraphic groups where different formations can be distinguished using unconformities mappable over the whole area of outcrop in the second post erosional stage developed during the quaternary nine stratigraphic levels are tentatively identified and are grouped in two phases of volcanic activity shields phase and pyroclastic cones phase data from 580 photogeologic lineaments as well as field data from 204 fault planes 195 with sense of movement 273 dykes and 45 volcanic alignments are presented the tectonic style of the deformations is brittle and polyphasic strike slip faults are dominant but normal and reverse faults are also present both the so called atlantic and african directions are well developed in trends of strike slip faults and volcanic indicators at least two deformation phases can be identified from the geometrical analysis of faults and from the stress tensor calculated using lineations on fault planes the reconstructed stress field responsible for the measured deformations changed orientation during the evolution of the island of lanzarote it is suggested that a permutation between principal stress axes 1 and 3 occurred subparallel to the length of the island between the pre erosional and post erosional stages

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

coherent intrusion complexes in large basaltic volcanoes a new structural model abstract highly concentrated coherent intrusion complexes consisting of thousands of small mafic intrusions occur in probably all major basaltic volcanoes and play an important role in volcano development magma excursions from the high level chamber travel laterally along a surface of neutral buoyancy at the margin of a complex and cause the complex to grow the limited distance however that narrow intrusions can propagate before becoming blocked causes complexes to be wedge like intrusive dike complexes underlie rift zones and asymmetric growth of the dike wedge causes rift zones of shield volcanoes to become non collinear and may initiate a third rift zone in the obtuse angle downbowing of stress trajectories across complexes causes dikes to be non vertical and results in axial subsidence intrusive sheet complexes form instead of dike complexes in volcanic systems that have a restricted ability to expand laterally and accommodate intrusions by expanding vertically instead downbowing of stress trajectories causes sheets to be non horizontal and this combined with subsidence increasing toward the thicker part of the sheet wedge produces the inward and inwardly increasing dip that characterizes cone sheet complexes this mechanism for cone sheets differs considerably from previously proposed mechanisms successive injections of sheets at the top of a sheet complex probably offers the most efficient means of powering a high intensity geothermal field such as the 5000 mw grimsvotn system in iceland it is inferred that similar mechanisms to those in major basaltic edifices operate in spreading ridges study of basaltic edifices has the potential to contribute significantly to the understanding of spreading ridges

monzonorites from rogaland southwest norway a series of rocks coeval but not comagmatic with massif type anorthosites duchesne j c wilmart e demaiffe d and hertogen j 1989 monzonorites from rogaland southwest norway a series of rocks coeval but not comagmatic with massif type anorthosites precambrian res 45 111 128 monzonorites members of the anorthositic suite of rocks are usually considered as residual after the formation of massif type anorthosites in rogaland s w norway they occur as large dykes intrusions and chilled margins to differentiated massifs emplaced during and soon after the main anorthosite massifs in granulite facies conditions ti p and fe are enriched in monzonorites and steadily decrease towards quartz mangerites the feo feo mgo ratios varying slightly during alkali enrichment bowen trend trace element spidergrams show deep troughs in rb th nb ta sr zr hf and ti the ree slightly decrease in the evolution with la yb s ratios about 9 and neutral to positive eu anomalies several occurrences however show highly contrasted trace element features sr isotope ratios st show a wide interval of variation 0 704 0 710 between the various dykes and intrusions without any correlation with the elements indicative of crustal contamination in the tellnes main dyke evolution towards acidic rocks occurs without contamination and variation in isr fractional crystallization with subtraction of apatite bearing noritic cumulates can account for the major and trace element evolution from monzonorite to quartz mangerite but is unable to explain the large differences between occurrences it is concluded that monzonorites cannot be comagmatic though coeval with massif type anorthosites they result from the crystallization of distinct magma batches possibly formed through partial melting of basic to intermediate rocks in the lower crust

baroclinic rossby wave forcing and barotropic rossby wave response to stratospheric vortex variability abstract an analysis is performed on the dynamical coupling between the variability of the extratropical stratospheric and tropospheric circulations during the northern hemisphere winter obtained results provide evidence that in addition to the well known charney and drazin mechanism by which vertical propagation of baroclinic rossby waves is nonlinearly influenced by the zonal mean zonal wind topographic forcing constitutes another important mechanism by which nonlinearity is introduced in the troposphere stratosphere wave driven coupled variability on the one hand vortex variability is forced by baroclinic rossby wave bursts with positive negative peaks of baroclinic rossby wave energy occurring during rapid vortex decelerations accelerations on the other hand barotropic rossby waves of zonal wavenumbers s 1 and 3 respond to the vortex state and strong evidence is presented that such a response is mediated by changes of the topographic forcing due to zonal mean zonal wind anomalies progres