age of the brookville gneiss and associated rocks southeastern new brunswick the brookville gneiss is a medium to high grade quartz feldspar biotite and hornblende quartz feldspar biotite gneiss found north and northeast of saint john new brunswick the green head group

an efficient and self adaptive approach for q value optimization the time invariant gain limit constrained inverse q filter can control the numerical instability of the inverse q filter but it often suppresses the high frequencies at later times and reduces the seismic resolution to improve the seismic resolution and obtain high quality seismic data we propose a self adaptive approach to optimize the q value for the inverse q filter amplitude compensation the optimized q value is self adaptive to the cutoff frequency of the effective frequency band for the seismic data the gain limit of the inverse q filter amplitude compensation the inverse q filter amplitude compensation function and the medium quality factor in the processing of the inverse q filter amplitude compensation the optimized q value corresponding gain limit and amplitude compensation function are used simultaneously then the energy in the effective frequency band for the seismic data can be recovered and the seismic resolution can be enhanced at all times furthermore the small gain limit or time variant bandpass filter after the inverse q filter amplitude compensation is considered to control the signal to noise ratio and the time variant bandpass filter is based on the cutoff frequency of the effective frequency band for the seismic data synthetic and real data examples demonstrate that the self adaptive approach for q value optimization is efficient and the inverse q filter amplitude compensation with the optimized q value produces high resolution and low noise seismic data

inverse q filter for seismic resolution enhancement a principal limitation on seismic resolution is the earth attenuation or q effect including the energy dissipation of high frequency wave components and the velocity dispersion that distorts seismic wavelets an inverse q filtering procedure attempts to remove the q effect to produce high resolution seismic data but some existing methods either reduce the s n ratio which limits spatial resolution or generate an illusory high resolution wavelet that contains no more subsurface information than the original low resolution data in this paper seismic inverse q filtering is implemented in a stabilized manner to produce high quality data in terms of resolution and s n ratio stabilization is applied to only the amplitude compensation operator of a full inverse q filter because its phase operator is unconditionally stable but the scheme neither amplifies nor suppresses high frequencies at late times where the data contain mostly ambient noise the latter property makes the process invertible differ

plutonic rock types series discrimination of various granitoid series and related rocks abstract the streckeisen qap diagram discriminates four characteristic type series among the large variety of granitoids associated in intrusions three of them integrate varied compositions from basic to acid terms 1 the calcalkaline series with its low k or trondhiemite medium k or granodioritic high k or monzonitic variants 2 the alkaline series with its characteristic syenitic members 3 the tholeiitic series deprived of k feldspars the fourth 4 corresponds to mobilizates associated with migmatites of varied composition but always quartz rich the generalization in the qapf system allowing the plotting of undersaturated alkaline series provides an excellent visual display of the major associations and trends for the plutonic rocks

removal of wavelet dispersion from ground penetrating radar data wavelet dispersion caused by frequency dependent attenuation is a common occurrence in ground penetrating radar gpr data and is displayed in the radar image as a characteristic blurriness that increases with depth correcting for wavelet dispersion is an important step that should be performed before gpr data are used for either qualitative interpretation or the quantitative determination of subsurface electrical properties over the bandwidth of a gpr wavelet the attenuation of electromagnetic waves in many geological materials is approximately linear with frequency as a result the change in shape of a radar pulse as it propagates through these materials can be well described using one parameter q related to the slope of the linear region assuming that all subsurface materials can be characterized by some q value the problem of estimating and correcting for wavelet dispersion becomes one of determining q in the subsurface and deconvolving its effects using an inverse q filter we present a

the gravity field in the central pacific from satellite to satellite tracking satellite to satellite doppler tracking between the ats 6 and the geos 3 spacecraft is used to measure the high degree and order gravity field over an 80 area in the central pacific ocean doppler tracking provides velocity measurements of geos 3 as a function of time which are easily converted to line of sight accelerations since the low degree and order gravity field is known well each geos 3 revolution is reduced relative to a twelfth degree and order field model the method is then capable of measuring wavelengths in the range from about 3500 to 1000 km accelerations computed along 40 revolutions roughly half of them descending and the others ascending can be contoured into a map of the gravity field at the geos 3 altitude of 840 km the dominant wavelength of the map is about 2000 km a comparison of this field with an altimeter derived geoid and the gem 10b gravity field shows good agreement since each map is essentially independent of the others this comparison is critical in establishing the validity of any of the maps each map shows virtually the same areas of positive and negative anomalies these areas are essentially the same in the central pacific as those found in our earlier study compared with surface amplitudes these anomalies are only one tenth as large at the geos 3 altitude this observation and the correlation of gravity with residual depth anomalies imply that the cause of some of these anomalies may be due to bumps in the upper surface of the lithosphere that are compensated at depths of about 30 100 km some of the anomalies apparently do not correlate with residual depth anomalies

origin and u pb geochronology of amphibolite facies metamorphic rocks miramichi highlands new brunswick the miramichi highlands of new brunswick are underlain by subgreenschist to greenschist facies sedimentary and volcanic rocks of the cambro ordovician tetagouche group and by amphibolite facies paragneisses amphibolites and felsic orthogneisses of the trousers lake and sisson brook suites new field geochemical and geochronologic data for the amphibolites and felsic orthogneisses suggest that they are high grade metamorphic equivalents of the tetagouche volcanic rocks and their associated intrusions amphibolites in the miramichi highlands occur as striped and unstriped varieties that possess chemical characteristics indicative of an igneous origin however the two types are compositionally distinct the striped amphibolites resemble volcanic arc tholeiites whereas the unstriped amphibolites are like within plate tholeiites the geochemically inferred tectonic origin of these amphibolites is compatible with a recently proposed intracontinental back arc tectonic setting for the tetagouche group felsi

geopotential orbit variations applications to error analysis the position and velocity errors of a near circular orbit due to geopotential uncertainty are developed in fourier series current satellite gravity models generate position uncertainties of up to 50 m alongtrack for close satellites 1000 km altitude in shallow resonance periods less than 5 days from coefficients of order 13 14 smaller radial errors are due to resonance and to first order terms poorly seen in current satellite geopotentials correlation of errors is strong by order and the same degree parity application of the development is made to 1 the prediction of errors for a future altimeter satellite 2 the capability of earth based tracking of a close mars orbiter in resolving that planet s gravity potential and 3 improvement of the resolution of the low degree geopotential from the geopotential research mission using tracking data from the global positioning system

precision geodesy and geodynamics using starlette laser ranging the starlette satellite launched by the french centre national d etudes spatiales in 1975 has provided an important means for deriving geodetic and geodynamic parameters from near earth satellite laser ranging data we report here on the development of a gravity field specialized for starlette designated pgs 1331 using the data from 1975 through 1978 we further report on the detailed analysis of the 1980 starlette laser ranging data for the estimation of tracking station coordinates polar motion gravitational constant gm and other parameters these analyses illustrate the improvement in our geodetic and geodynamic modeling provided by pgs 1331 data fits for 5 day orbital arcs have been improved from the level of several meters to a few decimeters comparisons of the station coordinate values derived from starlette with those from independent lageos solutions indicate an rms agreement of about 25 cm these analyses have provided an independent check of the lageos derived center of mass tracking station coordinates

regional differences in pb isotopic compositions of feldspars in plutonic rocks of the northern appalachian mountains u s a and canada a geochemical method of terrane correlation feldspar pb isotopic compositions from paleozoic tonalitic to leucogranitic caledonian plutons from the northern appalachian mountains of the u s a and canada range from nonradiogenic to radiogenic relative to the evolution curve of stacey and kramers 1975 pb isotopic values in the feldspars are generally independent of modal and major and trace element contents of the plutons plutons with the least radiogenic pb isotopic signatures northern group have intruded allochthonous rocks closest to the north american craton and plutons with the most radiogenic pb southern group have intruded avalonian basement feldspars from plutons in the central group have intermediate pb isotopic compositions between the northern and southern groups and do not define an isotopically unique group the predominant source of the felsic magmas was the continental lithosphere as indicated by the general pb isotopic similarity of the plutonic feldspars with either grenville or chain lakes basement in the case of the northern group and with avalonian basement rocks in the case of the southern group the source region for plutons in the central group may have contained a mixture of grenvillian and avalonian components plutons in the northern appalachians are as a group more evolved in their pb isotopic compositions relative to caledonian plutons in the british isles

a geopotential model from satellite tracking altimeter and surface gravity data gem t3 an improved model of earth s gravitational field gem t3 has been developed from a combination of satellite tracking satellite altimeter and surface gravimetric data gem t3 provides a significant improvement in the modeling of the gravity field at half wavelengths of 400 km and longer this model complete to degree and order 50 yields more accurate satellite orbits and an improved geoid representation than previous goddard earth models gem t3 uses altimeter data from geos 3 1975 1976 seasat 1978 and geosat 1986 1987 tracking information used in the solution includes more than 1300 arcs of data encompassing 31 different satellites the recovery of the long wavelength components of the solution relies mostly on highly precise satellite laser ranging slr data but also includes tranet doppier optical and satellite to satellite tracking acquired between the ats 6 and geos 3 satellites the main advances over gem t2 beyond the inclusion of altimeter and surface gravity information which is essential for the resolution of the shorter wavelength geoid are some improved tracking data analysis approaches and additional slr data although the use of altimeter data has greatly enhanced the modeling of the ocean geoid between 65 n and 60 s latitudes in gem t3 the lack of accurate detailed surface gravimetry leaves poor geoid resolution over many continental regions of great tectonic interest e g himalayas andes estimates of polar motion tracking station coordinates and long wavelength ocean tidal terms were also made accounting for 6330 parameters gem t3 has undergone error calibration using a technique based on subset solutions to produce reliable error estimates the calibration is based on the condition that the expected mean square deviation of a subset gravity solution from the full set values is predicted by the solutions error covariances data weights are iteratively adjusted until this condition for the error calibration is satisfied in addition gravity field tests were performed on strong satellite data sets withheld from the solution thereby ensuring their independence in these tests the performance of the subset models on the withheld observations is compared to error projections based on their calibrated error covariances these results demonstrate that orbit accuracy projections are reliable for new satellites which were not included in gem t3

gravity model improvement for seasat analysis of the data from the seasat altimeter a 10 cm precision instrument requires accurate knowledge of the radial position of the spacecraft for oceanographic applications such as the study of tides and ocean circulation as well as for geodetic applications initial orbit determinations using the best available geodetic and force models gave radial errors approaching 5 m the dominant source of this radial error was the gravity field model improvements in the gravity modeling were made by successively incorporating the seasat laser and unified s band ground tracking data the geos 3 altimeter data and finally the seasat altimeter data with the most recent model a set of spherical harmonic coefficients complete to degree and order 36 seasat ephemerides have been computed for an orbital arc length of 12 days with an rms radial accuracy of about 70 cm

radial variations of a satellite orbit due to gravitational errors implications for satellite altimetry the linear perturbations of the radius of a satellite orbit due to the geopotential are derived from these estimates are made of the radial orbit error due just to geopotential errors from current models employing only conventional satellite tracking data the estimates show that about an order of magnitude improvement in the satellite geopotential will be necessary to utilize the full accuracy of independent satellite altimeter measurements the linear perturbations are used to show that 1 a substantial improvement in the low degree geopotential is possible from the indirect use of seasat altimetry at track crossovers and 2 a separation of permanent sea topography and geoid may be possible from direct use of the heights along the track

accuracy estimate of geoid and ocean topography recovered jointly from satellite altimetry joint determination of the geoid and permanent dynamic sea topography is demonstrated by simulation from direct use of satellite altimetry the separation is feasible because of the disparities between the error spectra of the geoid and its unique perturbative effects as seen on the orbit the solution for the components of the permanent topography from 14 cm seasat altimetry promises to yield accurate results down to half wavelengths of about 1000 km present discrimination of this surface from disjoint satellite altimeter results appears to be at a scale near 4000 km the radial effects of uncertainties in the m2 ocean tide on the seasat orbit and altimeter measurements will probably be only a minor contaminant of the solution

time variations in the earth s gravity field detectable with geopotential research mission intersatellite tracking the geopotential research mission grm is a proposed system of two artificial satellites in tandem drag free polar orbits of low altitude 160 km designed for a detailed global mapping of the earth s gravitational and magnetic fields the mission should provide a large amount of new information about the gravity field particularly over continents resolving spatial variations in the gravity field as short as 100 km half wavelength however grm should also perform a much more difficult task the detection of time variations in the gravity field among the effects which produce changes in the field that are large enough to be detected by the intersatellite millimeter wavelength 1 s precision grm sensor are the following 1 rebound from ancient deglaciation 2 very large dip slip earthquakes 3 detailed ocean tides and 4 the seasonal growth and decline of continental glacial fields in particular many nonzonal as well as zonal components affected by postglacial rebound should be detected in a 6 month grm mission repeat passes over the fault zones of earthquakes similar to alaska 1964 chile 1960 or sumbawa 1977 should reveal signal changes due to their earth movements the effect of ocean tides on the grm signal should be readily detectable over a broad band of frequencies even if all but 10 of the tides are correctly modeled continued geophysical interest in these now largely unobserved phenomena warrants extension of the grm mission to somewhat higher altitudes

the crustal evolution of central scotland and the nature of the lower crust pb nd and sr isotope evidence from caledonian granites abstract the identification of the wide range of isotope characteristics and chemical heterogeneities within the sub continental mantle has demanded a re appraisal of the crustal evolution of many terrains a recent publication has suggested that such heterogeneities may also exist beneath scotland 1 this together with inadequate knowledge of the age and geochemical nature of the lower crust has fuelled the controversy of the relative involvement of mantle and crust in the formation of the caledonian granites 2 8 this paper reports 31 pb isotope analyses on feldspars from six granite complexes and four new nd and four new sr whole rock analyses these data demonstrate that a major source of the granites is the lower crust which is characterised by relatively unradiogenic sr pb and nd it is by inference old depleted in u and th and has a low th u ratio isotopic constraints suggest the sub grampian central scottish lower crust is dominated by grenville ca 1200 1000 ma age rocks in addition to an older scourian ca 2700 ma component the major episodes of crustal growth in central scotland occurred during the scourian and grenville orogenies the caledonian orogeny produced only limited crustal addition

archean inheritance in zircon from late paleozoic granites from the avalon zone of southeastern new england an african connection abstract in southeastern new england the narragansett pier granite locally intrudes carboniferous metasedimentary rocks of the narragansett basin and yields a monazite u pb permian emplacement age of 273 2ma zircon from the narragansett pier granite contains a minor but detectable amount of an older inherited component and shows modern loss of lead zircon from the late stage aplitic westerly granite exhibits a more pronounced lead inheritance permitting the inherited component to be identified as late archean such old relict zircon has not been previously recognized in proterozoic to paleozoic igneous rocks in new england and may be restricted to late paleozoic rocks of the avalon zone we suggest that the archean crustal component reflects an african connection in which old archean crust was underplated to the avalon zone microplate in the late paleozoic during collision of gondwanaland with avalonia

stable q analysis on vertical seismic profiling data abstractvertical seismic profiling vsp provides a direct observation of seismic waveforms propagating to various depths within the earth s subsurface the q analysis or attenuation 1 q analysis based on direct comparison between individual waveforms at different depths however suffers from the problem of instability commonly due to fluctuations inherent in the frequency spectrum of each waveform to improve the stability we considered frequency and time variations and conducted q analysis on an integrated observation first we transformed the time or depth frequency domain spectrum to a 1d attenuation measurement with respect to a single variable the product of time and frequency although this 1d measurement has a higher signal to noise ratio than the 2d spectrum in the time frequency domain it can also be used to further generate a stabilized compensation function then we implemented two q analysis methods by data fitting in a least squares sense to either the attenuation measurement o

q compensated pre stack reverse time migration in viscoelastic media with an irregular free surface pre stack reverse time migration rtm is a powerful tool that provides better imaging of complex geological structures than traditional migration methods an irregular free surface has significant impacts on the characteristics of seismic wave propagation and seismic imaging in mountain or basin areas in addition viscoelastic media produce a better representation of the earth than acoustic or elastic media a main feature of rtm in viscoelastic media is that it can consider compensation for p and s wave attenuation effects in this study we develop an approach for q compensated pre stack rtm in 2d viscoelastic isotropic media with an irregular free surface based on the boundary conforming method the viscoelastic model can be discretized to better match the irregular surface and interfaces the 2d second order viscoelastic equations and free surface boundary conditions are converted from the cartesian coordinate system to the curvilinear coordinate system the finite difference operators are applied to approximate the viscoelastic wave equations and the irregular free surface in the curvilinear coordinate system in addition the convolutional perfectly matched layer cpml absorbing boundary condition is selected to effectively suppress artificial reflections from the model boundaries in the numerical examples the snapshots shot gathers and q compensated pre stack rtm results show that our algorithm can obtain an accurate structure image in viscoelastic media in the presence of surface topography

the evolution of the avalonian plate abstract the avalon platform of newfoundland is the type locality of the avalonian plate that is characterized by late precambrian volcanic and clastic rocks marine at the bottom and terrestrial at the top all are intruded by 650 550 ma granites late precambrian rocks in the southern british isles are similar in both areas northeastern parts of the belt are affected by deformation and metamorphism that have orogenic aspects the orogeny is referred to as the avalonian in newfoundland and monian in britain to the southeast of the avalonian rocks in europe lies another late precambrian cadomian orogenic belt of rocks as a part of the pan african orogenic belt the cadomian and avalonian belts extend into north africa morocco since these belts are ophiolite bearing it is suggested that the plate was bordered by oceanic domains it is therefore proposed that a microcontinental volcanic arc that was generated in the late precambrian was orogenically deformed by collision with north america europe and africa and survived as a coherent terrain until the late carboniferous

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

sr and pb isotopes u and th chemistry of the alkaline monteregian and white mountain igneous provinces eastern north america the monteregian hills and younger white mountain alkaline intrusions were emplaced into the cambro ordovician sediments of the st lawrence lowlands and the folded and thrusted lower paleozoic sequence of the appalachian orogen age relations indicate that there is a fine scale structure to the igneous activity with slightly undersaturated to critically saturated rocks emplaced between 141 and 128 ma and strongly undersaturated rocks emplaced between 121 and 117 ma sr and pb isotopic data for the mantle derived alkali picrite alkali olivine basalt and basanite magmas indicate derivation from a depleted mantle similar to that which produces present day oceanic island basalts for the most isotopically primitive samples decay corrected 87sr86sr 0 7030 0 7037 206pb204pb 19 05 19 72 207pb204pb 15 56 15 65 and 208pb204pb 38 64 39 26 on pb sr isotope correlation diagrams the data define trends similar to those for mor basalts implying mantle heterogeneity which requires the presence of a component enriched in radiogenic pb relative to sr the interaction of these isotopically primitive magmas with the crust can be defined in terms of a three component system depleted mantle grenville age crust lower paleozoic age crust the granitic magmas were apparently derived from the lower paleozoic crust of the appalachian orogen for the mantle derived magmas th u ratios vary from 2 5 estimated ratio for morb source to 5 1 with the mean value near that of the bulk earth the variations in th u suggest mantle heterogeneity on a local scale and the high th u of some samples suggests that the mantle was enriched in incompatible elements shortly before melting the magmas derived by partial melting of the crust have th u of 3 3 to 8 7 and the higher ratios are associated with rocks crystallized from magmas that originated by melting of lower paleozoic sediments the sr and pb isotopic data support the conclusion of bellet al 1982 that the subcontinental mantle under eastern canada underwent a precambrian depletion event this depleted mantle apparently extends under the white mountain province and is isotopically similar to the mantle which gives rise to oceanic island basalts in contrast pb isotopic ratios for the new england seamount chain taras and hart 1983 which apparently represents the oceanic extension of this magmatic activity are significantly more radiogenic it is possible that a mantle plume provided the heat energy and perhaps metasomatic fluids to trigger melting in the subcontinental mantle whereas in the case of the oceanic extension the plume directly contributed to the observed magmatism as reflected in the more radiogenic pb ratios

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

grenvillian basement in the northern cape breton highlands nova scotia the northernmost cape breton highlands are underlain by the blair river complex a distinctive assemblage of basement rocks including felsic and mafic gneisses foliated gabbroic to granitic rocks