late mesozoic magmatism in svalbard a review abstract late mesozoic mafic igneous rocks are widespread across the arctic region and are collectively referred to as the high arctic large igneous province halip in svalbard the halip is represented by the diabasodden suite an extensive system of predominantly basic intrusive doleritic rocks associated lava flows are exposed on the far east of the archipelago two main igneous centres have been proposed 1 central spitsbergen and 2 the eastern svalbard dolerite belt spanning hinlopenstretet and the islands of edgeoya and barentsoya offshore seismic and magnetic data suggest a link between the svalbard and franz joseph land igneous exposures intrusions occur predominantly as sills up to 100 m thick and laterally continuous for up to 30 km dykes are present locally and range in thickness from

palaeomagnetism of some late mesozoic dolerite sills of east central spitsbergen svalbard archipelago summary two late mesozoic dolerite sills situated near agardhbukta on the east coast of vestspitsbergen and dated radiometrically at 100 4 myr bp have been sampled in five localities and subjected to detailed mineralogical and rock magnetic studies to determine the direction and origin of their magnetization although the sills lie outside the tertiary orogenic belt one locality no 4 has undergone strong hydrothermal alteration and a small part of another locality no 3 has also been affected a conventional procedure based on examination of zijderveld diagrams applied to specimens demagnetized by alternating fields and thermally yielded similar remanence directions at all five localities except at the altered part of locality 3 using a least squares computer method of analysis of step demagnetization data comparable directions were isolated from all localities including the altered part of locality 3 except in this last case all directions were reversed the adjusted mean direction obtained from this analysis is d 159 0 i 62 2 95 9 0 yielding a palaeomagnetic pole situated at 225 0 54 3 n comparable with pole positions obtained from other late mesozoic igneous rocks on spitsbergen and distinct from palaeopoles derived from mesozoic rocks in north america and eurasia this suggests that during the late mesozoic svalbard existed as a semi independent microplate

atmospheric torques during the winter of 1989 impact of enso and nao positive phases the axial component of atmospheric angular momentum aam reached a decadal minimum during the winter of 1989 when the cool la nina phase of the enso cycle and the positive phases of the north atlantic oscillation nao and the related arctic oscillation ao were active here we examine the global atmospheric dynamics associated with this event from the torque point of view it will be shown how mountain torques on north america south america and europe related to these oscillations led to the aam minimum partly compensated by a positive enso related mountain torque over asia the friction torque had more nearly equal positive and negative anomalies associated with enso and nao forcing respectively and made a smaller offsetting contribution to the global aam anomaly during this episode

aspects of pre tertiary paleomagnetism of spitsbergen and their tectonic implications abstract paleomagnetic investigations were carried out on cretaceous dolente dykes and sills permian limestones permo carboniferous limestones and lower devonian sandstones from different parts of spitsbergen detailed rock magnetic studies showed that the main magnetic minerals in dolentes limestones and sandstones are titanomagnetite magnetite and hematite respectively the rocks were demagnetized thermally and in alternating fields vector analysis of the demagnetization path separates the different components of nrm and establishes a characteristic remanence the paleomagnetic poles for cretaceous dolentes permo carboniferous limestones and lower devonian sandstones from spitsbergen are respectively 65 n 222 e 34 n 140 e and 12 n 135 e when compared with the european and north american apparent polar wander paths all spitsbergen poles he at a distance from both apwps suggesting that spitsbergen has been rotated and even translated in relation to europe during the opening of the labrador sea and greenland norwegian sea

two anisotropic layers in the slave craton abstract four years of recording global earthquakes using a broadband seismometer located at the ekati diamond mine revealed variations with earthquake azimuth in the arrival of sks phases these variations can be modeled assuming two distinct layers of anisotropy in the lithosphere the lower layer probably lies in the mantle and the anisotropy aligns with both north american plate motion and the strike of mantle structures identified by previous conductivity and geochemical analyses at n50 e the upper layer is hypothesized to result from regional structures in the uppermost mantle and the crust these trends are distinct from the mantle trends

paleomagnetic investigations of mesozoic and paleozoic rocks from svalbard abstract a paleomagnetic study of late mesozoic dolente dykes and sills and paleozoic sediments from spitsbergen the main island of the svalbard archipelago gives the position of the pole in the late mesozoic and paleozoic as distinct from the corresponding poles of europe and north america the paleozoic pole is to the south of corresponding poles for europe and north america the data suggest that svalbard has moved independently of europe and north america at least in the late mesozoic and thus might behave as a microplate or block

interannual atmospheric torque and el nino southern oscillation where is the polar motion signal 1 in this paper we investigate the atmospheric excitation of polar motion pm associated with the el nino southern oscillation enso phenomenon enso effects on length of day due to changes in the axial component of atmospheric angular momentum aam have long been recognized but identification of pm excitation with enso induced equatorial aam anomalies has proved more elusive here we use an appropriately modified form of the inverted barometer ib assumption to study enso related atmospheric torques arising from pressure loading on the earth s ellipsoidal bulge and mountains and from frictional wind stress over the earth s land and ocean covered surface the resulting dissipation torques which accommodate adjustment of the oceanic mass distribution to time variable atmospheric loading are found to be small the ellipsoidal torques have the largest amplitude reflecting the order of magnitude discrepancy between the height departures of the earth s bulge 20 km and its surface orography 2 km because of relatively uniform pressure covariances with the southern oscillation index over the continents for the largely land based x component and the uniform ib response for the largely ocean based y component however the enso related pm excitation arising from the ellipsoidal torques is reduced to an amplitude comparable with the sum of regional mountain torques from the individual continents the largest of these are generated over asia and antarctica arising from efficient coupling of enso related surface pressure anomalies with large scale orographic features the geometrical mitigation of the ellipsoidal torques classically expected to dominate equatorial aam forcing accounts for the lack of a detectable atmosphere driven polar motion response to enso

hydrological and oceanic effects on polar motion from grace and models 1 terrestrial water storage tws and ocean bottom pressure obp are major contributors to the observed polar motion excitations second only to atmospheric mass movement however quantitative assessment of the hydrological and oceanic effects on polar motion remains unclear because of the lack of global observations in this paper hydrological and oceanic mass excitations to polar motion are investigated using monthly tws and obp derived from the gravity recovery and climate experiment grace for january 2003 until december 2008 the results from this analysis are compared with hydrological model excitations from the european center for medium range weather forecasts ecmwf and oceanic model excitations obtained from the jet propulsion laboratory jpl using estimating the circulation and climate of the ocean ecco results show that the grace derived obp and tws better explain the geodetic residual polar motion excitations for the px component at the annual period while the grace obp and ecmwf hydrological angular momentum agree better with the geodetic residuals for the annual py excitation grace ocean and hydrology excitations better explain the geodetic residuals for the semiannual py excitation however the jpl ecco and ecmwf models better explain the intraseasonal geodetic residual of polar motion excitation in the px and py components the grace data demonstrate much higher intraseasonal variability than either the models or the geodetic observations

shear wave splitting continental keels and patterns of mantle flow in this study we investigated the origin of seismic anisotropy in the mantle beneath north america in particular we evaluated whether shear wave splitting patterns in eastern north america are better explained by anisotropy caused by lithospheric deformation anisotropy due to mantle flow beneath the lithosphere or a combination of both we examined new measurements of shear wave splitting from the missouri to massachusetts broadband seismometer array moma the north american mantle anisotropy and discontinuity experiment nomad as well as splitting parameters from several previous studies we developed a simple finite difference model that approximates mantle flow around a complex three dimensional continental lithospheric keel to evaluate potential anisotropy from mantle flow beneath the lithosphere in eastern north america we compared shear wave splitting observations to predicted splitting parameters calculated using this mantle flow model our results indicate that a significant portion of observed shear wave splitting in eastern north america can be explained by mantle flow around the continental keel however shear wave splitting patterns in a few regions of eastern north america indicate that a component of lithospheric anisotropy must exist particularly in regions containing the largest keel thicknesses for eastern north america as well as for splitting observations in australia europe and south america we favor a model in which anisotropy is controlled by a combination of both lithospheric deformation and subcontinental mantle flow

palaeomagnetism of some late mesozoic dolerite dykes of south spitsbergen summary opaque mineralogical studies of late mesozoic dolerite dykes of wedel jarlsberg land south spitsbergen show that the dykes have undergone a mild hydrothermal alteration the alteration probably took place at the time of consolidation of the dykes but may also have occurred as a side effect of tertiary orogeny which affected the western parts of spitsbergen seven of these dykes were sampled during two summer seasons when samples were collected from different exposures a conventional procedure based on the minimum scatter principle and study of zijderveld diagrams applied to 282 specimens demagnetized by alternating fields and thermally reveals several characteristic remanence directions in three dykes the directions are consistently reversed but one carries both normal and reversed remanence the reversed directions can be attributed to a geomagnetic field reversal in the late mesozoic and k ar dating of one of the reversed dykes gives an age of 110 5 myr bp in agreement with the known age of early cretaceous field reversal using a least squares method of analysis of step demagnetization low coercivity components not separated by the conventional procedure have been successfully isolated in two of the dykes the analysis applied to all the other dykes confirms the results of the conventional method yielding comparable mean directions of magnetization the conventional method applied to characteristic directions from five dykes gives a mean palaeomagnetic pole at 210 1 78 9 n ag5 3 5 and the least squares procedure applied to directions from six dykes yields a pole at 222 7 69 7 n ag5 7 9 the pole positions obtained agree with those obtained for spitsbergen dolerites by

hydrological and oceanic excitations to polar motion andlength of day variation summary water mass redistributions in the global hydrosphere including continental water storage change and non steric sea level change introduce variations in the hydrological angular momentum ham and the oceanic angular momentum oam under the conservation of angular momentum ham and oam variations are signi cant excitation sources of the earth rotational variations at a wide range of timescales in this paper we estimate ham and oam variations and their excitations to polar motion and length of day variation using soil moisture and snow estimates and non steric sea level change determined by topex poseidon satellite radar altimeter observations and a simpli ed steric sea level change model the results are compared with the variations of polar motion and lod that are not accounted for by the atmosphere this study indicates that seasonal continental water storage change provides signi cant contributions to both polar motion and lod variation especially to polar motion x and the non steric sea level change is responsible for a major part of the remaining excitations at both seasonal scale and high frequencies particularly in polar motion y and lod the good correlation between oam contributions and the remaining excitations shows that large scale non tidal mass variation exists in the oceans and can be detected by topex poseidon altimeter observations

new palaeomagnetic petrographic and 40ar 39ar data to test palaeogeographic reconstructions of caledonide svalbard new palaeomagnetic and petrographic data are presented from cambrian rocks of sw svalbard to test for the first time palaeozoic reconstructions of the major terranes of svalbard in the course of thermal demagnetization three chrm characteristic remanent magnetization components were identified which were labelled hornl hornm and hornh respectively on the basis of their different unblocking temperatures the hornm magnetization is related to the late ordovician silurian formation of the synmetamorphic s 1 foliation the hornm palaeopole 18 5 359 d p d m 5 8 11 4 plat 6 n matches exactly the silurian sectors of the baltica laurentia apparent polar wander paths after the closure of iapetus 455 415 ma the 450 ma 40 ar 39 ar age determination from mica ages obtained from the broad zone of mylonites along the billefjorden fault zone which separates the central and eastern terranes also suggests that the two terranes were eventually amalgamated by 450 ma the hornm vgp also lies very near the palaeopole derived from the middle proterozoic rocks of the eastern terrane ny friesland metamorphosed during caledonian time suggesting its close proximity to the study area central terrane the present study has shown that at least two of the major terranes of svalbard as defined by previous authors occupied similar geographical locations by silurian time and the previously proposed large scale late devonian left lateral displacements are not supported

atmospheric and oceanic excitation of the earth s wobbles during 1980 2000 1 because of the action of various geophysical excitation mechanisms the earth does not rotate about its figure axis so it wobbles as it rotates here the effectiveness of atmospheric and oceanic processes in exciting the earth s wobbles during 1980 2000 is evaluated using estimates of atmospheric angular momentum from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis project and estimates of oceanic angular momentum from the estimating the circulation and climate of the ocean ecco consortium s simulation of the general circulation of the oceans on intraseasonal timescales atmospheric surface pressure changes are found to be the single most effective process exciting the earth s wobbles explaining about twice as much of the observed variance as do either atmospheric wind or ocean bottom pressure changes and nearly 4 times as much of the observed variance as do oceanic currents however on interannual timescales ocean bottom pressure changes are found to be the single most effective process exciting the earth s wobbles explaining more than 5 times as much of the observed variance as do atmospheric wind and pressure changes combined and more than twice as much of the observed variance as do oceanic currents within the chandler band it is found that during 1980 2000 atmospheric and oceanic processes have enough power to excite the chandler wobble and are significantly coherent with it the single most important mechanism exciting the chandler wobble is found to be ocean bottom pressure variations atmospheric and oceanic processes do not appear to have enough power to excite the earth s wobbles to their observed levels on pentadal and longer timescales although series longer than the 21 yearlong series used here need to be studied in order to obtain greater statistical significance of this result

palaeomagnetic study of mesozoic basalts from scania southernmost sweden summary the mesozoic basalt necks of central scania southernmost sweden yield dual polarity palaeomagnetic directions decl 33 incl 66 n 15 and decl 225 incl 73 n 6 the combined mean with the negative directions reversed is decl 35 incl 68 n 21 the corresponding palaeopole is situated at lat 69 n 103 e this pole corresponds with an early jurassic pole for europe and with early jurassic poles for north america after closing of the atlantic the early jurassic age is in contrast with k ar datings ranging between 171 and 81 ma but is in agreement with datings based on microfossils found in tuffaceous layers connected with the basalts

paleomagnetism and the motion of large and small plates the focus of paleomagnetic research during past decades has varied greatly the first generation in paleomagnetism might be defined as beginning with the pioneering studies aimed at discovering whether the geomagnetic field has been a reliable reference frame for measuring and timing continental displacements an enormous effort followed in the form of individual paleomagnetic studies of cratonic rocks culminating with the construction of apw apparent polar wander paths for the continents which could be used to test paleogeographic reconstructions coupled with parallel research in marine geophysics and geology the refined apwp which result from this effort have helped to develop a reasonable first order history of cenozoic mesozoic paleogeography for the major plates

upper mantle stratigraphy beneath the southern slave craton a large teleseismic data set comprising 724 broadband three component p wave seismograms has been compiled for the southern slave craton with the objective of characterizing underlying mantle stratigraphy coherent p to s wave conversions are identified by simultaneously deconvolving seismograms as functions of epicentral distance and along theoretical moveout curves corresponding to possible mantle phases clear pds conversions are observed from the 410 and 660 km discontinuities at times that are only slightly faster than those predicted from the iasp91 model and over 1 0 s slower than corresponding times observed at other stations on the canadian shield and the south african kaapvaal craton the pds times show very little azimuthal variation implying an absence of major lateral velocity variations in the lithospheric mantle underlying the slave craton and adjacent wopmay orogen and taltson magmatic zone considered in light of other geophysical and geological evidence these results suggest that th

palaeomagnetic rock magnetic and mineralogical investigations of the lower triassic vardebukta formation from the southern part of the west spitsbergen fold and thrust beltk dudzisz and otherspalaeomagnetism of triassic rocks spitsbergen

numerical simulations of depth dependent anisotropy and frequency dependent wave propagation effects a numerical investigation of the effects of shear wave splitting for vertical propagation in a smoothly varying anisotropic medium is presented through forward modeling we predict the olivine lattice preferred orientation lpo developed in the oceanic upper mantle in response to the absolute plate motion apm we consider the effect of a change in apm similar to the one that presumably caused the kink in the emperor hawaii seamount island chain in the north pacific this results in an oblique orientation between lithospheric and asthenospheric anisotropy numerical simulations of shear wave propagation are used to estimate the characteristics of shear wave splitting ray theory does not account for coupling between shear waves in the depth dependent anisotropic medium due to the implicit assumption of high frequency a forward propagator technique for calculating waveforms and splitting parameters is used to assess frequency dependent effects the results show that ray theory is valid for estimating the splitting only for frequencies above 1 hz at frequencies more realistic for sks propagation apparent splitting parameters exhibit a 2 dependence on the incoming shear wave polarization back azimuth for certain back azimuth ranges shear wave splitting is very frequency dependent with apparent delay times ranging from 1 to 4 s and apparent fast polarization directions changing rapidly by up to 80 thus stacking of shear wave splitting measurements for largely different initial polarizations and frequencies should be avoided depth dependent anisotropy implies that shear wave splitting analyses will be sensitive to filtering anisotropic depth variations cannot be resolved unambiguously from splitting observations at relatively long periods 5 s it is not possible for instance to discriminate between smooth and abrupt transitions separating the anisotropic regions shorter period waveforms provide further information on the fine structure of anisotropic depth variations a comparison between splitting calculations and observations from hawaii suggests a divergent past apm direction or may indicate an alternative mechanism responsible for the lithospheric anisotropy

length of day variations caused by el nino southern oscillation and quasi biennial oscillation two prominent interannual atmospheric fluctuations the el nino southern oscillation in the troposphere ocean system and the quasi biennial oscillation in the equatorial stratosphere account for most of the observed interannual length of day lod variation from 1964 through 1987 with a relative contribution of about 2 to 1 thus the atmosphere lod connection extends from seasonal and shorter periods to interannual periods up to about 10 years

paleomagnetism of aptian albian sections from the northern apennines italy implications for the 150 100 ma apparent polar wander of adria and africa abstract we computed a new 120 to 100 ma high resolution apparent polar wander path apwp for adria from magnetostratigraphic studies in the northern apennines italy we analyzed 274 cores from three early aptian late albian sections of the marne a fucoidi fm belonging to the sedimentary succession deposited above the adria passive margin during meso cenozoic time to solve the problem of tectonic rotations induced during the apennine orogenesis we computed relative rotations between sections and realigned them into a common declination reference frame bosso italy these new data were added to the previous 150 125 ma segment computed from the same region satolli s besse j speranza f calamita f 2007 new 125 150 ma high resolution apparent polar wander path for adria from magnetostratigraphic sections in umbria marche northern apennines italy timing and duration of the global jurassic cretaceous hairpin turn earth planet sci lett 257 329 342 doi 10 1016 j epsl 2007 03 009 to get a very high resolution 100 to 150 ma apwp for adria the comparison of our apwp with the african apwp segment of besse and courtillot computed with 10 myr sliding window besse j courtillot v 2002 apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr j geophys res 107 doi 10 1029 2000jb000050 leads to the following conclusions 1 our segment after a 25 clockwise rotation of the bosso reference frame is in very good agreement with the african apwp as shown by a very similar time evolution of inclinations and declinations most often statistically indistinct 2 this agreement vindicates our previous model of structural unit rotation for older periods satolli s besse j speranza f calamita f 2007 new 125 150 ma high resolution apparent polar wander path for adria from magnetostratigraphic sections in umbria marche northern apennines italy timing and duration of the global jurassic cretaceous hairpin turn earth planet sci lett 257 329 342 doi 10 1016 j epsl 2007 03 009 3 the concept of synthetic apwp construction is strongly validated 4 the good agreement found strengthens the fact that adria has been a promontory of africa at the lithospheric level during late jurassic early cretaceous 150 100 ma affected by tectonic rotations linked to the apennines orogenic phases during neogene 5 our data evidence a possible ca 105 ma southward motion of adria undetected from classical african apwps finally we have not found evidence for reversals interrupting the long normal cretaceous superchron in our sections

a giant circumferential dyke swarm associated with the high arctic large igneous province halip abstract in this study we identify a giant circumferential mafic dyke swarm associated with the 135 75 ma high arctic large igneous province halip previously a halip giant radiating mafic dyke swarm with portions scattered across the canadian high arctic islands northern greenland svalbard and franz josef land was recognized in a pre drift plate tectonic reconstruction of the arctic region the radiating swarm has been interpreted to focus above a mantle plume responsible for halip magmatism the newly recognized halip giant circumferential swarm has a centre that is near the focus of the halip radiating system and hence is likely related to the halip plume elements of the circumferential swarm are located in each of the four regions where the radiating system is found the circumferential swarm has a quasi circular or slightly elliptical geometry an outer diameter of 1600 km and an arc of 220 it is one of the largest giant circumferential dyke swarms recognized on earth and could be linked to the outer edge of the flattening plume head it is also the first such swarm to have been identified by means of a plate tectonic reconstruction although giant circumferential dyke swarms appear to be relatively rare on earth possible analogues are common on venus and are also found on mars on venus giant circular or elliptical tectono magmatic features termed coronae are characterized by an annulus of graben or fissures and prominent topography some coronae include a radiating graben fissure system both radiating and circumferential graben may be underlain by dykes if so coronae could be analogues for terrestrial giant circumferential dyke swarms such as observed in the case of the halip

the two types of el nino and their impacts on the length of day at the interannual to decadal timescale the changes in the earth rotation rate are linked with the el nin o southern oscillation phenomena through changes in the atmospheric angular momentum as climatic studies demonstrate that there were two types of el nin o events namely eastern pacific ep and central pacific cp events we investigate how each of them affect the atmospheric angular momentum we show in particular that ep events are associated with stronger variations of the atmospheric angular momentum and length of day we explain this difference by the stronger pressure gradient over the major mountain ranges due to a stronger and more efficiently localized pressure dipole over the pacific ocean in the case of ep events