| 1. |
- Davis, J.L, et al.
(författare)
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Geodesy by radio interferometry: Effects of atmospheric modeling errors on estimates of baseline length
- 1985
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Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 20:6, s. 1593-1607
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of very long baseline interferometry data indicates that systematic errors in prior estimatesof baseline length, of order 5 cm for ~8000-km baselines, were due primarily to mismodeling of theelectrical path length of the troposphere and mesosphere ("atmospheric delay"). Here we discussobservational evidence for the existence of such errors in the previously used models for the atmosphericdelay and develop a new "mapping" function for the elevation angle dependence of this delay. Thedelay predicted by this new mapping function differs from ray trace results by less than ~5 mm, at allelevations down to 5° elevation, and introduces errors into the estimates of baseline length of •
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| 2. |
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| 3. |
- Widenfalk, Lennart, et al.
(författare)
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A multidisciplinary investigation of the Notträsk Gabbro, northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:2, s. 109-126
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Tidskriftsartikel (refereegranskat)abstract
- The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800-1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.
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| 4. |
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| 5. |
- Boldreel, Lars Ole
(författare)
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An attempt based on an interpretation of multichannel reflection seismic data to delineate sedimentary sequences, structures and evolution in the part of the Western Barents Sea 72° - 74°N and 10° - 17°E
- 1988
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is an attempt to throw further light on the structural development of the passive continental margin of the Western Barents Sea in the area from 72000'N to 74000'N and from 17000'E to 10000'E. It is based mainly on multichannel reflection seismics but available aeromagnetic, shipborne magnetic and free-air gravimetric data have also been analyzed. It seems from the results that the area between what is generally called the Senja fracture zone and the possible southernmost part of the Hornsund fault zone consists of a nonoceanic basement. The transition between the oceanic and the continental basement is placed adjacent to the Senja fracture zone and its northern continuation up to 740 N. The transition zone to the east of the Senja Fracture Zone in the area 720 50'N to 74000'N suggested in earlier works is here correlated with the development of a listric fault complex rooted in a detachment zone. The non-oceanic basement to the east of the Senja Fracture Zone is also examined and it is suggested that this basement is a stretched continental crust. A chronology for the sequences chosen has been established using the wells 711719-1 and 711719-2 located to the south of the area studied. The structural development of the margin has been dated on the basis of seven depth maps and four isopach maps of the sequences representing the time from the onset of the Tertiary to the end of the Oligocene. The main result is that the end of a major rifting phase corresponds to the beginning of the Paleocene while the onset of the sea floor spreading corresponds to the time interval from Early Eocene to Late Eocene. It appears from backstripping studies that the free-air gravity anomaly associated with the Senja Fracture Zone is probably due to the sediments loading an oceanic plate. This would mean that the Senja "Fracture Zone" is not really a fracture zone. It also seems that the seafloor spreading took place in an oblique northwards manner and that the oceanic basement closest to the Senja "Fracture Zone" and its northern continuation up to 740N is of Eocene age. If this interpretation is correct it would call for a modification of the 2-stage opening model of this area proposed in earlier works.
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| 6. |
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| 7. |
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| 8. |
- Das, U.C., et al.
(författare)
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Resistivity and induced polarization responses of arbitarily shaped 3-D bodies in a two-layered Earth
- 1987
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Ingår i: Geophysical Prospecting. - : Wiley. - 0016-8025 .- 1365-2478. ; 35:1, s. 98-109
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Tidskriftsartikel (refereegranskat)abstract
- Numerical computations using the integral equation method are presented for resistivity and IP responses due to arbitrarily shaped 3‐dimensional bodies in a layered earth. The unknown surface charge density distribution is expressed as the solution of Fredholm's integral equation of the second kind. Use of moment method (with pulse basis function and point‐collocation) yields the matrix equations for the unknowns. The contributions to Green's function are solved (a) analytically for the primary and (b) by convolution for the secondary contributions resulting in a fast algorithm. The further step of computing potential, apparent resistivity, chargeability etc., for any electrode system, is straightforward. Our results show a good agreement with those from finite difference methods and physical tank experiments. The CPU time is only 138 s on a super‐minicomputer for an apparent resistivity pseudo‐section, even with 96 elementary cells as used for discretization. A large number of models for different geological situations were studied; some are presented here.
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| 9. |
- Dyrelius, D., et al.
(författare)
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Bergarters fysik
- 1985
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Ingår i: Geofysik. - Uppsala : Svenska fysikersamfundet. - 9186344285
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Bokkapitel (populärvet., debatt m.m.)
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| 10. |
- Elming, Sten-åke
(författare)
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A palaeomagnetic study of Svecokarelian basic rocks from northern Sweden
- 1985
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Ingår i: Geologiska föreningens i Stockholm förhandlingar. - : Informa UK Limited. - 0016-786X. ; 107:1, s. 17-35
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Tidskriftsartikel (refereegranskat)abstract
- This palaeomagnetic investigation comprises basic rocks from six localities from the Svecokarelian zone in northern Sweden. Most of the pole positions in this study and other reported poles of Svecokarelian and post-Svecokarelian rocks fall within an approximately 12 degrees wide band running from east to west representing ages of magnetizations from 1880-1700 to ∼ 1530 Ma. Thermal demagnetizations of specimens of the probably oldest massifs indicate a possible backward continuation of the polar wandering path. Mineralogical studies of thin sections of the rocks show ore symplectites and myrmekitic textures indicating a slow rate of cooling at least at the end of the rock formation. Signs of metamorphism are demonstrated by the existence of secondary minerals, including magnetite, not related to late magmatic alterations. The distribution of site means as well as the change of directions of the remanence vectors during thermal demagnetization can be explained by a slow rate of cooling and where signs of metamorphism exist by partial remagnetization of the rock. This study has, apart from the palaeomagnetic results, demonstrated the difficulty of correlating radiometric ages with ages of magnetization
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