joint two dimensional dc resistivity and seismic travel time inversion with cross gradients constraints it is now common practice to perform collocated dc resistivity and seismic refraction surveys that complement each other in the search for more accurate characterization of the subsurface although conventional separate dc resistivity and seismic models can be diagnostic we posit that better results can be derived from jointly estimated models we make the assumption that both methods must be sensing the same underlying geology and have developed an innovative resistivity velocity cross gradients relationship to evaluate the structural features common to both methods the cross gradients function is incorporated as a constraint in a nonlinear least squares problem formulation which is solved using the lagrange multiplier method the resultant iterative two dimensional 2 d joint inversion scheme is successfully applied to synthetic data serving as validation tests here and to field data from collocated dc resistivity and seismic refraction profiling experiments and also compared to conventional separate inversion results the joint inversion results are shown to be superior to those from separate 2 d inversions of the respective data sets since our algorithm leads to resistivity and velocity models with remarkable structural agreement

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

a geodetic view on isostatic models before the background of more accurate and denser gravity data it is worthwhile to reassess geodetic isostasy currently in geodesy isostatic models are primarily applied to gravity reduction as needed by geoid and gravity modeling the selection of the isostatic model is based on four criteria isostatically reduced gravity anomalies should be 1 geophysically meaningful 2 easy to compute 3 small smooth and therefore easy to interpolate and 4 the indirect effect i e the change of potential and gravity due to isostatic mass replacement should be small in this study we analyze free air anomalies as well as isostatic anomalies based on the airy heiskanen model and on the pratt hayford model in regard to these criteria several facts suggest that free air anomalies are the most realistic type of isostatic anomalies they reflect the actual isostatic compensation are easy to compute and their indirect effect is negligibly small however they are not smooth due to the fact that local topographic loads are only partially compensated smoothness can be achieved by introducing either a mathematical low pass filter or a hydrostatic isostatic model such as the airy heiskanen or the pratt hayford model in both cases the resulting isostatically reduced gravity anomalies fulfill all requirements in order to improve the numerical efficiency a new mathematical description of the pratt hayford model is formulated the level of smoothing with respect to free air anomalies is analyzed in global and regional contexts it turns out that the mechanism of mass compensation in regions of large topographic loads is better described by the airy heiskanen model whereas the pratt hayford model is more suitable for regions of deep ocean trenches

ut variation of internal sq currents and the oceanic effect during 1980 march 1 18 summary ut variation of the internal part of sq currents is examined using the geomagnetic data during 1980 march 1 18 and the effect of the ocean is found the ratio of the internal currents to the external increases when the external current vortex comes above the atlantic and pacific oceans and the internal current vortex shifts to the oceans when the external vortex approaches the edge of the oceans the existence of the ocean increases the total induced current by about 30 per cent and this amount is consistent with model calculations for sq by previous workers

statistical characteristics of the day to day variability in the geomagnetic sq field 1 day to day variability in the geomagnetic sq field is studied by using the magnetic data from a meridian chain of magnetometers along 120 e longitude the method of natural orthogonal components noc or eigenmode analysis is applied to separate the sq variation from complicated disturbances the first eigenmode with the largest eigenvalue represents fairly well the sq variation with a conspicuous day to day variability in the daily range for the stations on the same north or south side of the sq current system focus the day to day variations show a positive correlation in contrast for the stations on the different sides of the sq focus they show a negative correlation suggesting an important role of latitudinal shift of the sq current system focus to the day to day variability in the sq daily range the sq daily range is correlated with the magnetic indices ap and dst in a peculiar way on some severe disturbed days noticeable enhancements of the sq are observed implying increases in the ionospheric conductivities and or tidal wind velocities on other severe disturbed days however dramatically reduced sq variations occur suggesting dominant effects of the disturbance dynamo process

electric currents in the ocean induced by the geomagnetic sq field and their effects on the estimation of mantle conductivity summary electric currents induced in the ocean by the geomagnetic sq field are simulated for a system which consists of a uniform geocentric sphere of finite conductivity and a non uniformly conductive thin shell sphere representing the sea land distribution the simulation results show that the induced currents have maximum intensity in the northern pacific ocean at 22 hr ut and enhance the total induced fields by about 60 per cent even when the external current vortex is located above the eurasian continent the internal current vortex is enhanced by about 10 per cent by the existence of the ocean next we have checked the effects of the electric currents in the ocean on the estimation of the mantle conductivity and found that ignoring the currents induced in the shell gives a less conductive and shallower estimation of the mantle conductor furthermore an apparent dependence of the conductivity on the depth appears because of the effects of the currents induced in the shell even if the mantle is a uniform conductor the conductivity and depth are estimated to be 0 1 sm 1 and 500km respectively from the data analysis for the 1 day period variation field of the p12 mode if the effects of the currents in the shell are ignored but it should be 1s m 1 and 780 km if the effects are considered

deformation resulting from regional extension during pluton ascent and emplacement central sierra nevada california solid state foliation lineation small scale folds and domainal shear zones have developed in preexisting granitic and minor metasedimentary wallrock during a combined deformation involving a regional extensional strain and ascent and emplacement of the mt givens pluton mgp mylonite is common throughout much of the 1 2 km wide 10 km long shear zone with ultramylonite best developed near the contact with the mgp which itself lacks significant solid state deformation migmatization accompanies ultramylonite formation in the northern half of the zone but both these features are poorly developed or absent in its southern half where the shear zone is distributed over a wider area strain estimates across the shear zone using microgranitic enclaves as markers show a positive gradient and an increasing ratio of simple shear pure shear towards the mgp microprobe analyses on hornblende and plagioclase yield pressure and temperature estimates of 3 5 kb and 680 c respectively during shear zone formation at least at its late stages of development zircon pb u and 40 ar 39 ar ages constrain timing of the high temperature movement on the shear zone to 90 ma essentially the age of the mgp although movement immediately prior to that time appears likely we speculate that a regional extensional shear zone was developing prior to the emplacement of the mgp which as it ascended heated the wallrock facilitating both further strain in the zone as well as buoyant rise of the pluton along the zone the mgp was near its critical melt fraction during the last several kilometers of its ascent and could have possessed sufficient viscosity strength to impose a weak shear strain on the shear zone rocks although most of the foliation and extensional features in the zone are probably related to the regional strain field late stage folding of the foliation is attributed to shouldering aside of the wallrock by the mgp during the last increment of its ascent and final emplacement

global induction and the spatial structure of mid latitude geomagnetic variations summary a pre requisite for more precise estimates of the electromagnetic response of the earth is a better knowledge of the origin and spatial structure of geomagnetic time variations with periods of a few hours to several years the period range from four hours to four days is particularly crucial for constraining upper mantle conductivity models but is difficult to analyse because of overlapping contributions from current systems with different spatial scales a period band centred on two days has been isolated from two years of hourly mean values recorded at up to 130 observatories plots of the coherence between pairs of records of the same component of the field at different observatories as a function of the station separation prove to be a valuable diagnostic tool they show that two groups of sources contribute to this part of the spectrum one group has a spatial scale in excess of 10 000 km dominates the geomagnetic north xm component but produces no east ym component it can be satisfactorily modelled by a p01 spherical harmonic and must be generated by fluctuations in the symmetric magnetospheric ring current the spatial coherence of the second group falls to zero in a distance of 5000 7000 km and can be predicted by a stochastic source model for which the autocovariance scale length is 7000 km the spatial structure of the two groups is further investigated using the principal component technique of egbert booker 1989 the spectrum is dominated by the largest eigenvalue and the eigenfunctions corresponding to this mode show the expected p01 source behaviour the modes which correspond to the next largest eigenvalues are organized into foci approximately 10 000 km across the vertical fields associated with these modes are of low amplitude at mid latitudes but increase steeply beyond 50d estimates of the p01 response based upon the horizontal and vertical fields recorded at a single station will be biased by the contribution from the higher order modes the magnetic observatory network is incapable of describing them properly on a global basis and only the european subarray is sufficiently dense to form locally valid response estimates

mafic enclaves in granitoid intrusions a catastrophic model of rheological behaviour the significance of mafic enclaves as indicators of magma mixing processes between juxtaposed felsic and mafic magmas is evaluated from a rheological point of view a qualitative model for explaining strain and morphological changes in the enclaves has been developed on the basis of the catastrophe theory mafic enclaves in intrusive granitoids commonly behave as physical systems that can be described using a cusp catastrophe model their behaviour is characterized by bimodality divergence and sudden changes which are properties typical of this model accordingly the presence of mafic enclaves showing variable strain and morphology within the same granitoid intrusion would be indicarive of mutual interaction and mingling between mafic and felsic magmas due to the characteristics of these processes it is not possible to establish unambiguous age relationships between the two magmatic components

a comprehensive model of the quiet time near earth magnetic field phase 3 summary the near earth magnetic field is caused by sources in the earth s core ionosphere magnetosphere lithosphere and from coupling currents between the ionosphere and the magnetosphere and between hemispheres traditionally the main field low degree internal field and magnetospheric field have been modelled simultaneously with fields from other sources being modelled separately such a scheme however can introduce spurious features especially when the spatial and temporal scales of the fields overlap a new model designated cm3 comprehensive model phase 3 is the third in a series of efforts to coestimate fields from all of these sources this model has been derived from quiet time magsat and pogo satellite and observatory hourly means measurements for the period 1960 1985 it represents a significant advance in the treatment of the aforementioned field sources over previous attempts and includes an accounting for main field influences on the magnetosphere main field and solar activity influences on the ionosphere seasonal influences on the coupling currents a priori characterization of the influence of the ionosphere and the magnetosphere on earth induced fields and an explicit parametrization and estimation of the lithospheric field the result is a model that describes well the 591 432 data with 16 594 parameters implying a data to parameter ratio of 36 which is larger than several popular field models

deep structure of the western south african passive margin results of a combined approach of seismic gravity and isostatic investigations abstract the passive margin of the south atlantic shows typical features of a rifted volcanic continental margin encompassing seaward dipping reflectors continental flood basalts and high velocity density lower crust at the continent ocean transition probably emplaced during initial seafloor spreading in the early cretaceous the springbok profile offshore western south africa is a combined transect of reflection and refraction seismic data this paper addresses the analysis of the seismic velocity structure in combination with gravity modelling and isostatic modelling to unravel the crustal structure of the passive continental margin from different perspectives the velocity modelling revealed a segmentation of the margin into three distinct parts of continental transitional and oceanic crust as observed at many volcanic margins the lower crust is characterised by a zone of high velocities with up to 7 4 km s the conjunction with gravity modelling affirms the existence of this body and at the same time substantiated its high densities found to be 3100 kg m 3 both approaches identified the body to have a thickness of about 10 km yet the gravity modelling predicted the transition between the high density body towards less dense material farther west than initially anticipated from velocity modelling and confirmed this density gradient to be a prerequisite to reproduce the observed gravity signal finally isostatic modelling was applied to predict average crustal densities if the margin was isostatically balanced the results imply isostatic equilibrium over large parts of the profile smaller deviations are supposed to be compensated regionally the calculated load distribution along the profile implies that all pressures are hydrostatic beneath a depth of 45 km

seasonal and longitudinal variations of the solar quiet sq current system during solar minimum determined by champ satellite magnetic field observations 1 vector magnetometer observations from the challenging minisatellite payload champ satellite are used to determine the solar quiet sq current system during the recent solar minimum observations from 2006 to 2008 are combined and after removal of a main field model and accounting for field aligned currents the longitudinal and seasonal variation of the sq currents are determined through the method of spherical harmonic analysis comparison with sq currents derived from ground based magnetometers in the african european longitude sector reveals similar amplitudes and seasonal variations indicating that the champ observations can reliably determine the sq current system the seasonal variation is consistent with prior observations during solar minimum conditions and in the northern hemisphere exhibits a primarily annual variation with peak currents during local summer the seasonal variation in the southern hemisphere is characterized by a semiannual variation with the maxima occurring around the equinoxes significant longitudinal variations are also observed and they display a seasonal variability during northern hemisphere summer the predominant feature at local noon is a wave number 1 variation in longitude during the remainder of the year a wave 3 longitudinal structure is observed at this local time the longitudinal variations are considered to be due to a combination of the orientation and strength of the geomagnetic field as well as the tidal winds in the lower thermosphere variations in tidal winds due to nonmigrating tides may influence the dynamo generated electric fields and currents resulting in the observed longitudinal variations of the sq current function

the lunar geomagnetic tide at night summary hourly values from 1964 65 of the three geomagnetic elements from a large number of stations have been analysed for the various lunar components these were combined to examine in detail the seasonal and diurnal variations of the lunar geomagnetic tide at night comparison of the values for the oceanic component calculated in a similar way to malin 1973 showed good agreement between sunspot maximum and minimum years when seasonal changes were included the d and z elements gave evidence of a lunar modulation of magnetic field aligned currents entering the ionosphere in auroral regions the effects of these currents appeared to extend as far away as the equator changes in their amplitude during the night also suggest a relation to auroral processes there is a just resolved nighttime equatorial electrojet h component and a quite large lunar h component in the auroral regions

electric currents in the ocean induced by a model dst field and their effects on the estimation of mantle conductivity summary electric currents induced in the ocean by the external dst fields are simulated for a system which consists of a uniform geocentric sphere of finite conductivity and a non uniformly conductive thin shell sphere representing the sea land distribution the effect of the ocean on the dst field is smaller than that on the geomagnetic sq field however fairly strong currents are induced is the antarctic ocean and these currents partly explain the anomalous behaviour of the geomagnetic response observed at hermanus especially for the variations of periods of less than two days

oblique diapirism the criffel granodiorite granite zoned pluton southwest scotland abstract strain trajectories strain gradients and quartz c fabrics have been used to propose an emplacement history of the criffel zoned pluton strain has been estimated from the microdioritic xenoliths included in the outer granodiorite textural criteria have been used to complete the pattern of strain variations throughout the pluton strain gradients are found to be related to the granodiorite granite boundary zone with highest strain towards the northeast side of the pluton giving an asymmetric horseshoe pattern quartz c fabrics allow two strain histories to be distinguished within the pluton an early coaxial flattening in the granodiorite followed by a non coaxial deformation in the granite and the adjacent granodiorite these features are interpreted as the result of an oblique diapiric intrusion of the inner granite into the partially emplaced and crystallized granodiorite

electromagnetic induction effects by the solar quiet magnetic field at satellite altitude we show that magnetic fields induced by a near earth ionospheric source can produce at a satellite altitude of 400 km an induced magnetic anomaly field with an amplitude of 2 3 nt at dawn and dusk local times and 3 4 nt at noon local time our results are based on an earth model which has an upper 4 km thick shell with a laterally varying electrical conductivity representing the distribution of continents and oceans the upper shell overlies a one dimensional mantle with a radially varying electrical conductivity in some regions the induced anomaly field does not change sign between dawn and dusk and appears static when sampled by a satellite such as magsat this induced anomaly field could explain some of the weak oceanic static anomalies observed in satellite global magnetic anomaly maps

geomagnetic quiet day selection based on published literature and the response to a questionnaire sent to geomagnetic field ionospheric and magnetospheric researchers several methods of choosing periods of quiet conditions based on geomagnetic records as well as other observed parameters have been identified caveats with respect to using geomagnetic indices to select quiet periods include the following 1 geomagnetic disturbances are strongly local even if the data from all available observatories indicate quiet behavior there is the distinct possibility that some other location not sampled may be disturbed 2 geomagnetic indices are convenient but imperfect indicators of geomagnetic activity indices based on a quiet day reference level have uncertainties comparable to the threshold value for quiet conditions indices representing average conditions during a 24 hr ut day may not be appropriate 3 geomagnetic activity does not fully reflect the range of possible factors that influence the ionosphere or magnetosphere

multiple injections of magmas along a hercynian mid crustal shear zone sila massif calabria italy abstract syn tectonic late hercynian granitoids emplaced at mid crustal level through multiple dyke injections are well exposed in a 1 km long section in the southern sila massif calabria italy the fieldwork study permitted us to reconstruct the following order of emplacement i granodiorites with euhedral kfs megacrystals grd1 in the main text and heterogranular granodiorites with coarse rounded pl and kfs in a fine grained biotite rich matrix grd2 ii granodiorites with a nearly homogeneous grain size grd3 iii tonalite and iv granite both in the wall rock represented by migmatitic paragneisses and in the deformed granitoids the foliation attitude is substantially homogeneous striking about n140 with a dip of 50 60 to the ne the magmatic lineation is defined by the preferred alignment of euhedral feldspars parallel to the mineral lineation observed in the host rocks micro and meso structural analyses indicate that foliation evolved from melt present to solid state conditions feldspar tiling s c structures type structures c axis quartz orientations commonly suggest a top to the west sense of shear during magma injection and deformation under decreasing temperatures age of magma emplacement is constrained by u pb datings at 304 300 ma coeval with the regional metamorphic peak foliated granitoids and wall rock are intruded by poorly foliated hbl gabbro and finally by undeformed leucogranite pegmatite and felsic porphyritic dykes new u pb datings of the last intrusion event indicate an age of emplacement of 281 8 ma providing a minimum estimate for the end of the shear strain at mid crustal level

gravity anomalies crustal structure and flexure of the lithosphere at the baltimore canyon trough seismic and gravity anomaly data have been used to examine the long term mechanical properties of the lithosphere beneath the baltimore canyon trough a 15 km deep sedimentary basin in the rifted u s atlantic margin seismic data constrain the crustal structure at the time of rifting as well as the amount of sedimentation and erosion that has occurred the gravity effect of the initial crustal structure sedimentary loading and erosional unloading have been computed and compared to the observed free air gravity anomaly the best fitting model is one in which the elastic thickness of the lithosphere te changes at the east coast magnetic anomaly landward of the anomaly te is significantly smaller than previously reported values for continental or oceanic lithosphere of the same thermal age seaward of the anomaly however te follows the depth to the 450 c oceanic isotherm which also describes the response of oceanic lithosphere to seamount and oceanic island loads these results are interpreted as indicating that the shelf part of the trough is underlain by continental lithosphere which following rifting did not acquire any significant long term strength

the planetary scale distribution of telluric currents and the effect of the equatorial electrojet an investigation by canonical gds the planetary scale distribution of electrical currents in the earth is still largely unknown the role of the oceans for long period hours to days inducing electromagnetic fieldsbe of external origin has been investigated by several authors while the role of telluric current channelling from the planetary viewpoint is still far from a satisfactory understanding canonical geomagnetic depth sounding gds analysis can yield locally a direction parallel to the strike of a telluric current density flowing in a region around the recording site and which also has the property of being the most relevant source for the internal origin fieldbi observed at the given site at the given frequency the use of such local information from 64 geomagnetic observatories is discussed here in a study to infer evidences of a the role of the polarization properties ofbe and b the role of the telluric current channelling within conductivity anomalies relevant to the planetary scale circuitry the results show clear evidence of the influence of the equatorial electrojet on the polarization ofbe in a latitudinal band between 15 20 latitude there is also evidence that thebe associated with the equatorial electrojet produces telluric currents which flow at a much shallower depth than the skin depth to be expected in the case of a plane earth this implies that the parkinson planes in these regions reflect the conductivity structure underground more than the polarization ofbe due to the equatorial electrojet further it clearly appears that some regular planetary scale pattern of telluric currents plays a more significant role than current channelling within some conductivity anomalies of fixed strike close to some geomagnetic observatories finally the number of observatories used in this study appears to be insufficient to deduce any information concerning a seasonal evolution of the telluric current pattern on a planetary scale

spherical harmonic analysis of geomagnetic tides 1964 1965 the mathematical forms chosen for analyses of s q and l by seventeen different authors are reviewed on the basis of the review and on consideration of the ionospheric dynamo theory and the hough function structure of wind velocities in the upper atmosphere a mathematical model is chosen that includes two more terms than the recent analysis by malin 1973 hourly mean values from 130 magnetic observatories for the i q s ys international quiet solar years 1964 and 1965 were prepared in machine readable form and analysed the solar and lunar transient magnetic variations were evaluated together with the lunar elliptic magnetic tide and the seasonal change at one and two cycles per year for all magnetic tides spherical harmonic analyses were made of the phase law tides and the smaller partial tides altogether 94 different spherical harmonic analyses were completed for a total of ten different magnetic tides two of the ten tides are the solar and lunar magnetic tides usually denoted s and l respectively the results are tabulated in a form that distinguishes between eastward and westward moving terms which is suitable for the evaluation of phase angle differences and amplitude ratios between internal and external parts malin s ocean dynamo calculation has been applied to the lunar and lunar elliptic magnetic tides the spherical harmonic coefficients are compared in some detail with those of malin 1973 for years of high sunspot activity the magnetic tidal potential associated with a given atmospheric tidal mode is derived theoretically and used to obtain an estimate of the hough function components of the solar and lunar semi diurnal atmospheric tides at ionospheric levels from the corresponding magnetic tidal potential

the oligocene xanthi pluton northern greece a granodiorite emplaced during regional extension the xanthi pluton is one of a series of oligocene subduction related granodiorites in northern greece its emplacement was controlled by major faults it is located on the ene trending kavala komotini fault zone which probably originated as a strike slip fault geophysical data show that the pluton is laccolith shaped extending many kilometres south of the fault andesitic dykes several million years older than the pluton indicate a ne sw directed extensional stress field mineral lineations plunging to the sw reflect continued extension during cooling of the pluton subsequent jointing and dykes of aplite and lamprophyre reflect continued extension although this could result from extensional pull apart at a bend during dextral strike slip motion on the kavala komotini fault there is no evidence for subsequent strike slip deformation furthermore two similar laccolithic plutons are unrelated to the kavala komotini fault and the regional extent of thick oligocene sediments suggests an extensional environment during the extension that created a ramp space along the listric fault bounding the xanthi basin into which the granite was intruded the kavala komotini fault acted as a transfer fault reactivation of early joints occurred during late oligocene early miocene compression faults within the pluton parallel to the kavala komotini fault accompanied extension during neogene basin formation emplacement of subduction related magma into ramp space developed along listric faults to produce laccolith like plutons may be a common feature of back arc extension

lunar daily geomagnetic variations in new zealand summary lunar daily geomagnetic variations l exhibit distinctive behaviour at many sites near coasts in this study data from an array of three component magnetometers that operated for a four month summer period at 22 sites throughout new zealand are used to examine l the chapman miller method is used to determine the four main luni solar harmonics of l at each site analysis of 3 5 years of data from the geomagnetic observatory at eyrewell indicates that the array data produce representative values of l separation of the dominant lunar semidiurnal harmonic l2 into parts of oceanic and ionospheric origin indicates near uniform ionospheric contributions to the x and y field components at all sites with peak values occurring within 3 hours of lunar transit the ionospheric contribution to the 2 field component is smaller and suggests secondary electric currents flowing in the deep water to the north east and south west of new zealand the oceanic contribution to l tends not to be significant for x and y its amplitude for 2 is greatest in the eastern north island and in the south western south island and its phase angle for z is locally consistent throughout the north island and in the south western south island the difference between the phase angles that characterize these northern and southern regions is about 180 this pattern suggests near parallel in phase electric currents flowing in the deep water to the north east and south west of new zealand in response to tidal flows this is in agreement with both the general pattern seen in the united kingdom and lunar daily geomagnetic variations observed under the tasman sea and in eastern australia where the magnetic effects of tidal flows in shallow coastal waters are secondary to those from more distant deep waters the oceanic contribution to l2 might be used to estimate the poorly known tidal flows in the deep water off new zealand

a diurnal modulation of the lunar tide in the upper atmosphere analysis of geomagnetic data from several stations in the equatorial region shows that the amplitude of the lunar semimonthly tide frequently does not have the expected symmetry about noon in its diurnal variation there is a distinct tendency for larger amplitudes in the morning at many stations this effect is largest in equinoctial months though there are regional differences analysis of data from different years confirms its presence the interaction between solar and lunar tides in the middle atmosphere may be responsible for the observed modulation

a process oriented approach to modeling the gravity signature of continental margins the gravity anomaly at a continental margin can be regarded as the result of all the processes that have shaped it through time these include rifting sedimentation and magmatic underplating this article discusses a new process oriented approach to gravity interpretation which uses seismic constraints on sediment thickness and the underplate at continental margins to estimate the gravity anomaly that is associated with rifting sedimentation and magmatic underplating by comparing the calculations to the observed free air gravity edge effect anomaly we have been able to determine the elastic thickness and crustal structure and to provide an estimate of the location of the ocean continent transition since crustal structure is a proxy for the amount of heating that occurred at the time of rifting the approach has important implications for the deep water hydrocarbons industry

the structure of the lunar semi diurnal pressure tide l2 the hough structure of the lunar semi diurnal tide l2 p in surface pressure is estimated using joint weightings by area and probable error structure on annual and lloyd seasonal scales with new data global representations on seasonal and annual scales of the l2 wave in both spherical harmonic and hough function forms are presented for the haurwitz cowley dataset enlarged by the more recent tidal determinations of hutchings and palumbo these are mainly for southern hemiphere island locations the asymmetric hough eigenfunction terms h32 are considerably larger than previously estimated both annually and seasonally a possible artefact of the earlier data analysis technique they are consistent and identified with the well known difference in phasing and amplitude of l2 by hemisphere the dependence of the hough structure on the order of the fitting and on the more extreme residuals is examined it is stable for the smallest models spherical harmonic terms up to degree 6 and order 3 to removal of the largest residuals from a first fitting and to the two largest datasets seasonal changes in the hough structure are discussed the asymmetric results appear consistent with early frictional thermal interpretations on the seasonal variation of l2 but the sensitivity of l2 to upper air temperature structure is not consistently shown in the analyses for the main mode h 2 2 copyright 2005 royal meteorological society

induction in arbitrarily shaped oceans vi oceans of variable depth we present calculations of t he electric currents induced in a model ocean by the 24 hr sq variation the model has realistic bathymetry and represents a further step of a consistent approach to oceanic induction in which we have introduced various complexities in order of priority the solution obtained is compared with our previously published results for the case of an ocean of realistic shape and uniform depth it is found that the major shelf seas considerably modify the pattern of elect ric current circu lation in the oceans of the southern hemisphere the consistent nature of the method of matched outer and inner expansions which we have used is also discussed it seems probable that other methods not limited to finding an outer solution and consequently more complicated will at best only produce an outer solution since in practice the relatively coarse mesh necessarily used in the computation of realistic global problems precludes a fine resolution of the coastal bathymetry finally the meaning of the internal and external legendre coefficients and their relationship to sq over the oceans is briefly discussed

shear margins continent ocean transform and fracture zone boundaries as exploration extends into deeper water it has become more important to understand the nature of the earth s crust beneath offshore sediments that is heat flow and related source rock potential usually require that sediments be deposited over continental crust hence delineating the boundary between oceanic and continental crust becomes important the material in this article was originally presented at the workshop the crust and its structure at seg s recent annual meeting in calgary these results part of a larger dissertation research project also have been presented to several oil and gas exploration companies in houston

why no anomaly is visible over most of the continent ocean boundary in the global crustal magnetic field abstract it is generally believed that an anomaly should be expected over the continent ocean c o boundary in the global magnetic anomaly maps however such maps prepared at satellite altitude do not show an anomaly over most of the c o boundary we address this issue by a forward modelling technique we use a geographic information system gis technique to integrate information of the various geological units of continents and oceans the seismic crustal structure and standard susceptibility values of the rock types and compute a global vertically integrated susceptibility vis model in addition a remanent magnetisation model is used for the oceanic crust combining the induced and remanent magnetisation models the crustal field anomaly is predicted at a satellite altitude of 400 km for spherical harmonic degrees 16 80 the results show that an anomaly is indeed not predicted over the c o boundaries where the oceanic crust is flanked by continental regions phanerozoic in age we demonstrate that largely a c o anomaly over these regions is not even expected in the global magnetic anomaly map for degrees 1 80 confirming that it is not a long wavelength feature masked by the core field an anomaly however is predicted over some parts of the c o boundary where the flanking geological provinces over the continents are precambrian in age we argue that the vis values for the continents and oceans are largely comparable and therefore no anomaly is expected over most of the c o boundary

quiet ionospheric currents of the southern hemisphere derived from geomagnetic records a special selection of extremely quiet 1965 geomagnetic daily variation records from north america europe central asia and east asia was used to determine monthly spherical harmonic analysis coefficients representing the sq fields from these regions the coefficients permitted a separation of the external and internal contributions to the daily variations month by month behavior of the equivalent external current system and contours of the daily range of this current showed regional differences in amplitude and location of the equivalent ionospheric currents with seasonal change current foci locations reached 35 to 42 geomagnetic latitude in summer and 18 to 35 in winter with a regional dependence the largest daily range of external current was 14 6 104 a in north america 15 3 104 a in europe 13 7 104 a in central asia and 12 3 104 a in east asia continental differences in the behavior of the current seemed to be explained by the relative position of the geographic and geomagnetic poles with respect to these regions

day to day variability of geomagnetic hourly amplitudes at low latitudes summary a study of the variability of the amplitude of sq at a fixed hour from one day to the next at nine stations from the dip equator to about 22 north of it has produced interesting results the amplitude and sign of the variability change virtually randomly making the mean practically zero the variability occurs at all hours of the day its magnitudes in the components d h and z have the same diurnal variation which peaks in the noon period like sq h in low latitudes and a weak seasonal variation that peaks at the june solstice local summer it is demonstrated that changes in the current intensities of the equatorial electrojet eej and the worldwide part of the sq w sq current layers have contrasting phases and can sometimes be in antiphase indeed the changes are mostly independent inclusion of the magnetic element d revealed that the eej current system has not only an east west but also a north south component the study shows that the meridional component of the eej current intensity evidenced at the kodaikanal and annamalainagar stations is an integral part of the zonal component at trivandrum this confirms the results of rastogi 1996 and validates those of onwumechili 1997 the results suggest that ionospheric conductivity mainly controls the magnitude while the electric field and ultimately winds mainly control the phase and randomness of the day to day variability of the hourly amplitudes of sq the random component is attributed to local and or regional atmospheric winds probably of gravity wave origin

the secular variation of the geomagnetic field and the shape of the earth abstract we generalize on the planetary scale some results by mundt aubert and kas yanenko for the european area we prove that the secular variation sv shows a scatter with respect to some smooth trend which correlates with a suitable surface specifically with its radial distance from the earth s centre at each geomagnetic observatory obtained by interpolating the ocean floors and by extrapolating them inside the continental areas such a surface has been selected from 30 different ones including the geoid by a statistical analysis of 20 160 possible plots a very tentative interpretation can be proposed in terms of a possible role of long period telluric currents flowing in the asthenosphere mostly zonally and in an equatorial belt this conclusion however could find additional confirmation by means of some suitable further investigations and harder thinking for which a few suggestions are proposed here furthermore an interesting by product is the evidence of an apparent and clear periodicity of 11 3 years in the geomagnetic yearly values which also needs to be discussed further

mid crustal shear zone evolution in a syn tectonic late hercynian granitoid sila massif calabria southern italy by means of petrogrological meso and microstructural analyses the fabric of a syn tectonic late hercynian k feldspar megacryst bearing granodiorite is described in this paper the granodiorite was emplaced at 293 ma within migmatitic paragneisses which had reached the regional peak metamorphic conditions at 304 300 ma the granodiorite and the migmatitic paragneisses are both affected by the same ductile shear zone in the core of the shear zone mylonites show a clear grain size reduction and microstructures related to deformation at high to medium temperature conditions migmatitic paragneisses foliated granodiorites and mylonites mostly show concordant lineation and foliation orientations in addition the preferred orientation of euhedral feldspars in granodiorites indicates that the fabric anisotropy started to develop in the magmatic state these features strongly suggest that shear deformation was active during crystallisation of granitoids and continued under subsolidus conditions in wall rocks and mylonites kinematic indicators such as and type porphyroclasts s c fabrics shear bands and quartz c axis orientations suggest a top to the w sense of shear this is similar to the magma flow direction indicated by the tiling of euhedral feldspar megacrysts in granodiorites shear deformation developed preferentially by partitioning of strain in the granodioritic crystal mush geobarometry indicates that deformation took place at middle crustal levels p 400 500 mpa whole rock white mica rb sr geochronological analysis of an undeformed pegmatite crosscutting the mylonitic foliation provided an age of 265 ma timing of deformation is therefore bracketed between 293 ma and 265 ma

the quiet daily variation in the total magnetic field global curves most magnetic mapping exercises involve measuring the amplitude or total field component of earth s magnetic field removing the time varying part of the field is a task of data reduction and the most common time variation is the quiet daily variation sq it is thus valuable to have for reference type curves of the quiet daily variation in the total field to meet this need global data obtained during the 1965 international year of the quiet sun have been used to derive type curves describing the sq variation of the total magnetic field in addition to the traditional field components as for the traditional components the total field curves show significant seasonal and latitudinal variability in amplitude and phase the effect of the equatorial electro jet is clearly evident in both hemispheres of the globe there are bands of reduced amplitude in total field signal between the equator and the path of the sq focus these bands here termed the total field doldrums persist throughout the year

the annual variation of the night time values of the geomagnetic field summary in this paper we present the results of an analysis of the variation of period of one year in night time h data the analysis indicates that this annual variation comprises of two components 1 a component whose amplitude depends on latitude and is of opposite phase in the two hemispheres this component is assumed to be due to the change of the latitude of the ring current caused by the solar wind as originally proposed by malin isikara 1976 2 a smaller component which in a given year has an amplitude and phase that is approximately the same at all latitudes but which may change from year to year its origin is not known but it is suggested that it may be found in the modulation of a distant current such as the cross tail current of the night time magnetosphere

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

variability of the equatorial electrojet its relations to the sq current system and semidiurnal tides average diurnal and seasonal variations of the horizontal geomagnetic element delta h are examined the semiannual variation in equatorial electrojet strength is found to disappear in afternoon hours this may be related to changes in the latitude of the sq current system focus during the day this in turn may be caused by a superposed semidiurnal tide and may also explain delta h variations at stations near the focus

solar and lunar geomagnetic variations in the northwestern part of turkey summary hourly mean values of x y and z components of the geomagnetic field from two observatories and the total intensity f of the geomagnetic field from eight monitoring stations were analysed to study the behaviour of solar and lunar geomagnetic variations in the northwestern part of turkey the chapman miller method was applied to the data first as a whole and then by grouping it to lloyd s seasons to calculate seasonal dependence of the harmonics amplitudes of solar and lunar harmonics increase from winter months to summer months the first two harmonics of both solar and lunar origins were calculated annually to compare with sunspot relative numbers to see annual and semi annual variation the solar harmonics show very good sunspot dependence but lunar harmonics do not it means that both ionospheric and ring current systems have an important role in the formation of solar harmonics but lunar harmonics are affected by ionospheric current system only in the northwestern part of turkey we would not expect and we do not find much ocean effect at these observatories since they are all remote from oceans with significant tides

the long period electromagnetic response of the earth summary the techniques of complex demodulation and spherical harmonic analysis have been used to examine the time frequency and location dependent properties of the long period electromagnetic response of the earth fourteen years of daily three component magnetic field data recorded by 18 permanent geomagnetic observatories were used to estimate the response in the period range 2 200 day it is found that lateral conductivity inhomogeneities within the earth notably the oceans have a considerable effect on the observed response even at these long periods

daily geomagnetic variations on the iberian peninsula summary mean hourly values of the horizontal and vertical components of the geomagnetic field at six observatories on the iberian peninsula were analysed to study seasonal and spatial behaviour of the solar and lunar ionospheric and oceanic daily geomagnetic variations the results are tabulated and their characteristics are discussed the influence of local oceanic effects on the lunar oceanic contribution at the peninsular observatories is noted in particular the spatial behaviour of the lunar oceanic contribution is considered whereas the mean value for the peninsula is consistent with that expected according to an existing model for electric currents in the eastern atlantic ocean individual values are not the influence of tide in the mediterranean sea of water currents in the strait of gibraltar and of local effects in the atlantic ocean is proposed as the reason for this behaviour

wavelet analysis of the coherence between bouguer gravity and topography application to the elastic thickness anisotropy in the canadian shield summary we use a wavelet transform to compute the local and azimuthal variations of the coherence between bouguer gravity and topography in eastern canada the isotropic coherence is calculated by averaging the wavelet spectra from optimally overlapping 2 d morlet wavelets having an isotropic spectral envelope in adjacent directions within 180 defining the so called fan wavelet the isotropic wavelet coherence spectrum is inverted to obtain local estimates of the elastic thickness te of the lithosphere we calculate the anisotropic coherence by restricting the fan wavelet over an azimuthal range of 90 the direction of maximum coherence is diagnostic of the direction of preferred isostatic compensation or the direction where the lithosphere is weakest the coherence is inverted using the theoretical response of a thin anisotropic plate model we have carried out extensive tests on synthetic topography and bouguer gravity data sets to verify that 1 the wavelet method can recover te for simple models with either homogeneous or spatially variable rigidity patterns and that 2 the method can determine azimuthal variations in the 2 d coherence for homogeneous models with anisotropic te we have used data from the eastern canadian shield to infer the variations in te and the anisotropy of the coherence the relative variations in te show trends similar to those obtained in previous studies that used different spectral methods the wavelet transform gives te values between 30 and 120 km te is generally high 80 km throughout eastern canada lower values 30 60 km are found in the eastern grenville province in the northern appalachians and in the superior province in the great lakes region the high values found in hudson bay are consistent with previous studies of elastic thickness and models of basin subsidence the direction of maximum coherence obtained from the wavelet method is also consistent with our previous results obtained with the multitaper method and shows that the weak mechanical axis is perpendicular to the fast seismic axis where seismic anisotropy has been detected

an introduction to quiet daily geomagnetic fields on days that are quiet with respect to solar terrestrial activity phenomena the geomagnetic field has variations tens of gamma in size with major spectral components at about 24 12 8 and 6 hr in period these quiet daily field variations are primarily due to the dynamo currents flowing in the e region of the earth s ionosphere are driven by the global thermotidal wind systems and are dependent upon the local tensor conductivity and main geomagnetic field vector the highlights of the behavior and interpretation of these quiet field changes from their discovery in 1634 until the present are discussed as an introduction to the special journal issue on quiet daily geomagnetic fields

chemical and isotopic evidence for major mass transfer between mafic enclaves and felsic magma abstract in both the strontian and criffell zoned granitoid plutons certain chemical elements notably k rb ca sr and pb display a correlation between their concentration in microdiorite enclaves and their concentration in the immediately enclosing host granitic rock this appears to represent the effects of post incorporation mixing and exchange between the enclave and its host magma enclave initial 87 sr 86 sr ratios are indistinguishable from those of the host while enclave initial 143 nd 144 nd ratios are systematically more radiogenic establishing that these enclaves are not melt segregations nor restite the isotopic data are in agreement with the chemical data in indicating that sr is almost entirely derived from the host despite clear evidence of major mass transfer of alkali metals alkali earths and transition metals a comparison of the concentrations and ratios of hfse and ree and nd isotopic ratios with those of a number of potential starting protoliths allows the enclave precursors to be positively discriminated in this regard enclave hfse and ree compositions may allow for models of granitoid production by the injection of hot mantle derived magmas into the crust to be tested

spatiotemporal sampling of sq induced geomagnetic responses at leo satellite altitude for a radially conductive earth summary a new simulation tool is introduced for extracting earth conductivity information from geomagnetic satellites in low earth orbit leo such as champ swarm and potential follow on missions theoretical reconstruction of spherical harmonic spectra of global universal time ut geomagnetic field maps is analysed an idealized regular solar daily variation field is assumed along with its induced counterpart from a radially stratified earth solar quiet sq spectra can be reliably reconstructed from discrete time series of measurements sampled daily within a fixed ut window a single leo satellite should be in orbit for at least 1 yr under quiet time conditions to ensure accurate spectral reconstruction of an sq geomagnetic spectrum the length of the daily sampling window and random day to day variability in the sq source strength have only minor effects on spectral reconstruction the shape of the spectra and spectral ratios are independent of radial mantle conductivity further research employing 3 d forward modelling of induction in a laterally heterogeneous earth with more realistic and complete external source descriptions is advocated the new simulation tool should prove valuable to planners of future multisatellite geomagnetic missions as well as scientists interested in analysing and interpreting satellite induction signals

studies of worldwide secular trends in the solar daily geomagnetic variation summary secular changes in the solar geomagnetic variation at 11 observatories with a worldwide distribution have been studied the secular changes at uk observatories were found to be large numerical calculations details of which are described in this paper agree in predicting the large changes at uk observatories the numerical calculations also predict a large secular change in sq at hermanus in all elements this would be expected as the main field at this station shows a large secular change the secular change in sq observed at hermanus is however found to be fairly small compared with that observed at the other stations

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

a method for the determination of the initial shapes of deformed xenoliths in granitoids abstract measuring strain from deformed xenoliths is problematic due mainly to the large initial shape variations of these markers a method is described which allows mean initial shape to be determined for a number of xenolith populations by displaying their logarithmic ranges log rfmax log rfmax on a range diagram the diagram contains a check on validity and allows bad samples to be recognised xenolith data from a deformed granite in northwest ireland is analysed using the method

deformation of mylonites in palm canyon california based on xenolith geometry abstract an analysis of xenoliths in granodiorite and mylonites of the peninsular ranges batholith in southern california documents large deformation with von mises equivalent strains ranging from 1 to 4 from the geometry of xenoliths in mylonites it is concluded that much of the deformation occurred by flattening if deformation had been homogeneous the 800 m thick mylonite sequence would have extended originally over more than 10 km contrary to xenoliths associated with ballooning diapirs these in santa rosa mylonites show much larger strains and are elongated in the lineation direction it is proposed that the overall deformation pattern is consistent with a top to the west shear displacement but most of the strain in the santa rosa mylonites was produced in flattening during emplacement of the partially solidified batholith the large deformation may have produced folds that have coalesced with the foliation to accommodate the strain

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

evidence for significant granite space creation by the ballooning mechanism the example of the ardara pluton ireland the emplacement mechanism of the ardara granite a caledonian pluton located on the northwestern seaboard of ireland has been a widely cited and a key point of reference in the debate about the granite space problem for nearly half a century early models related its subcircular tailed shape concentric foliation pattern and concentrically deformed envelope to diapirism it was subsequently reinterpreted using strain data as a ballooning pluton that was created by 70 in situ expansion at the emplacement site and was later cut by a regional shear zone recently it was the leading example in a wide ranging review of forcefully emplaced plutons of this type and was reinterpreted as a series of nested diapirs associated with only modest amounts 30 of forceful space creation but a large component of inferred early block stoping we report the results of the complete remapping and extensive collection of new structural data from this 8 km diameter normally zoned three phase calc alkaline pluton we confirm the existence of the steeply inclined internal foliation pattern and that it was formed in the magmatic state although this and the outline of the pluton are modified by late stage high temperature solid state regional transcurrent shear zones along two of the pluton contacts structural mapping has failed to identify a macroscopic lineation in the magmatic foliation planes and this is confirmed by strain determinations using mafic enclave populations and magmatic crystal separations for the magmatic state deformation that show nearly pure flattening type strains k 0 strains measured by these techniques show an apparently smooth gradient increasing outward toward the pluton contacts from an inner low strain zone we argue that these features together with the simple normal petrographic zonation a lack of small scale structures that would indicate the pluton had moved up relative to the wall rocks and an exposure level that is not in the roof zone are inconsistent with diapirism either singly or multiply but are most easily explained by a ballooning emplacement mechanism synmagmatic shear sense data from both the pluton and the adjacent country rocks indicate however that within the overall context of radial ballooning there was a limited amount of late stage nonradial northward injection of magma an inversion of the deformed enclave and crystal spacing strain determinations and strain determinations within the country rocks suggest that more than 80 of the volume of the pluton was accommodated by the ballooning mechanism

the ionospheric sq current system obtained by spherical harmonic analysis 1 an earlier comprehensive analysis of geomagnetic tides by winch is revisited to display changes in the current systems with season and longitude the data used come from the quiet sun years 1964 1965 we choose to present some total equivalent current systems being the sum of the external and internal parts derived in the spherical harmonic analysis the latitudes and local times of the current system foci are generally in agreement with other workers the amplitudes of the current system vortices follow an annual variation with maximum in summer the longitude variations of the vortex amplitudes vary as the inverse of the magnetic field strength at both equinoxes but have different variations at the solstices other longitude maxima which have been reported in the equatorial electrojet intensity were not found we examine in detail the invasions of the summer current systems across the equator identifying these as signatures of field aligned currents facs the tilting of current contours with respect to the equator is interpreted as being due to midday facs as others have found the identification of afternoon facs is more difficult the seasonal swap over of fac directions occurs not in september but in october november

the significance of microgranitoid enclave shapes and orientations abstract enclaves are often incorrectly used to measure magmatic strains in plutons we emphasize that microgranitoid enclaves are not like other ellipsoidal markers used to determine strain for the following reasons 1 adjacent enclaves may form at different times and different places and initially have non spherical shapes with axial ratios up to 2 7 2 the final shapes and orientations of enclaves are a complex function of a initial shape and temperature of enclaves b subtle changes in composition melt percents volatiles grain sizes and thus temporally variable viscosity contrasts between the enclave and magma c a competition between strain and interfacial energies and d deformation path which may include internal strain and rigid rotations caused by magma flow during ascent convection expansion chamber boundary processes and tectonism 3 enclaves spend much of their time in magma as relatively rigid objects and thus rigidly rotate and potentially break apart rather than strain at matrix strain rates 4 in some instances enclaves do not record or track finite strain because of the above final enclave populations are heterogeneous and the use of single enclaves or enclave populations as strain markers violates many assumptions needed to complete strain analyses on the other hand a comparison of the preserved characteristics of igneous layering mineral fabrics and carefully evaluated enclave fabrics including internal mineral alignment in enclaves may provide qualitative data on the changing magnitude and kinematics of magmatic strains

national geophysical data center candidate for the world digital magnetic anomaly map marine and airborne magnetic anomaly data have been collected for more than half a century providing global coverage of the earth furthermore the german champ satellite is providing increasingly accurate information on large scale magnetic anomalies the world digital magnetic anomaly map project is an international effort to integrate all available near surface and satellite magnetic anomaly data into a global map database teams of researchers were invited to produce candidate maps using a common pool of data sets here we present the national geophysical data center ngdc candidate to produce a homogeneous map the near surface data were first line leveled and then merged by least squares collocation long wavelengths were found to agree surprisingly well with independent satellite information this validates our final processing step of merging the short wavelength part of the near surface data with long wavelength satellite magnetic anomalies

currents associated with abnormal quiet days in sq h summary declination data have been analysed on nqds and aqds for the years 1963 64 65 such an analysis indicates that there is a larger southward current in the morning and a larger northward current in the afternoon on nqds than aqds in both the northern and southern hemispheres the strength of this current is found to be imf dependent taken in conjunction with the previous analyses of the h data it is concluded that on aqds the sq h amplitude is affected by a reduction in the current of a large current vortex which extends over both hemispheres and is part of the normal sq h current system such a current is driven by diurnal winds variations in the strength of the wind thus contributing to the day to day variability of the sq h amplitudes aqds therefore represent days of small amplitude in the general day to day variability the imf dependence arises due to complicated current systems that flow on aqds and which are associated with high latitude phenomena and generally have their focus at latitudes 60 similar to those found by takeda araki

the use of gravity anomaly data for offshore continental margin demarcation analysis of gravity anomaly data can be an effective and economical means of demarcating the world s offshore continental margins

global induction by sq and dst sources in the presence of oceans bimodal solutions for non uniform spherical surface shells above radially symmetric earth models in comparison to observations summary we pursue in this paper the following goals 1 detailed study of the ocean eiect on geomagnetic elds excited by sq and dst sources in spherical earth models the investigated period range is from 6 hr to 10 days oceans and continents form a thin shell of variable conductance above a layered deep structure allowing for leakage currents from and into the shell 2 development of an interpretation scheme for the estimation of the resistivity ol of the lithosphere 3 application of this scheme to estimate ol from a comparison of calculated and observed sq harmonics at coastal sites we conduct a number of model calculations with simpli ed hemispherical shells and with realistic shells for the world s oceans and continents deriving their variable conductance from the ocean depth at sea and assuming a uniform value of 400 s on land with inclusion of continental shelfs from these model studies we draw the following conclusions 1 variations of o l in the uppermost 100 km of the deep structure signi cantly change the vertical magnetic surface eld z near oceans 2 ocean eiects in the horizontal magnetic surface elds x and y are quite negligible on land for sq therefore radially symmetric earth models can be used to determine the external sq source eld from a spherical harmonic analysis of x and y on land 3 with realistic shell models it is possible to reproduce the anomalous coast eiect in z of sq a two step interpretation scheme is presented to estimate the resistivity ol of the lithosphere in step 1 we determine the spherical harmonic coe cients of the external sq source eld using the observed sq variations in x and y and a presumed earth model of uniform shell conductance to separate their external and internal parts in step 2 we derive model elds with various trial values of ol for a realistic surface shell excited by the external source eld from step1 we choose the most likely value of ol that for which the rms mis t between observed and calculated z variations is smallest ourobservational data are the rst four sq harmonics of the four equinoctial months of 1964 as derived from the mean daily variations of quiet days at 76 observatories z observations at 12 coastal observatories lead us to the conclusion that a global estimate of lithospheric resistivity ol is of the order of 10 000 m