摘要:

Several intrusive and extrusive rock complexes in Skåne in southern Sweden have been dated by Rb—Sr and K—Ar age-determination methods. The dated complexes comprise two sets of dolerite dykes, massifs of syenite and plugs of basalt. The basalt necks belong to at least two groups aged 167 ± 4 Ma and 108 ± 3 Ma, respectively (K—Ar). North-west-trending dolerite dykes dated by the K—Ar method yielded an average age of 294 ± 4 Ma. A shale adjacent to a dolerite dyke was studied, in order to ascertain the thermal effect of the dyke on the surrounding argon system. Syenite massifs associated with the tectonic boundary between south-eastern and south-western Sweden have a Rb—Sr isochron age of 1210 ± 38 Ma and an initial87Sr/86Sr ratio of 0.7055 ± 0.0027. K-Ar datings of these rocks and their minerals demonstrate extensive argon diffusion, which causes apparent K—Ar ages of 800–900 Ma. NNE.-trending dolerite dikes have a Rb—Sr isochron age of 1600 ± 230 Ma at an initial87Sr/86Sr ratio of 0.7033 ± 0.0015. The K-Ar ages have been disturbed by the opening of the system and fall in the interval between 800 and 1500 Ma. The syenite massifs contain xenoliths of NNE.-trending dolerite and consequently the Rb—Sr age of the syenites defines a minimum age for the dolerites.

ISSN:0016-786X    

DOI:10.1080/11035897609454371

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The adductor-muscle scar patterns ofRoundyellaandScrobiculadiffer greatly and do not allow us to retain these genera among the Scrobiculidae. A new family (Roundyellidae) is proposed. Both families should be assigned to independent superfamilies (Scrobiculacea and Roundyellacea). These are tentatively referred to Podocopa, due to the presence of calcified inner lamella of primitive type and (inScrobicula) marginal pore canals. It is suggested that the marginal structures in these groups have occurred independently.

ISSN:0016-786X    

DOI:10.1080/11035897609454372

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The present north-eastern and south-western limits of the East European Platform are formed by long and deep faulted troughs with some elements of strike-slip movements. Between these westerly converging, craton margins, four other subparallel tectonic zones are proposed, with a mutual spacing of a few hundred kilometres. The western part of the platform is thus divided into five major blocks, which are further transected by some series of faults with mainly north-westerly and north-easterly, northerly and easterly trends. Geological and geophysical records indicate the pervasive character of these major tectonic zones, in which intermittent magmatic activity and mineralization of heavy metals is found. The lineaments are considered to have persisted from Archaean time and been re-activated during successively younger orogenies in the platform. This pattern of tectonic zones is assumed to represent a structural anisotropy, imprinted in the crust and the upper mantle at a relatively early period in the history of the earth.

ISSN:0016-786X    

DOI:10.1080/11035897609454373

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The paper describes a method of determining the velocity in rock of pressure waves and shear waves. When the pressure waves and shear waves are known, the elastic constants of the rock can be calculated. The elastic constant has been correlated to the fissure frequency, which is known to influence the elastic constants. This survey was carried out on a highly migmatized, sediment gneiss.

ISSN:0016-786X    

DOI:10.1080/11035897609454374

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

The Caledonides and the Baltic Shield, with its area of Fennoscandian land uplift, are tectonic features of high significance, as regards the structure, dynamic history and present dynamics of the earth's crust in Scandinavia. The Caledonides represent the remnants of an old orogenesis, which most probably took place in the collision zone between drifting lithospheric plates 700–400 m.y. ago. The Baltic Shield is an ancient crustal block, indicating folding older than 1500 m.y. The Fennoscandian land uplift is regarded as an isostatic re-adjustment after the last ice age, but there are evidences of a continuous but much smaller land uplift since the Caledonian. In order to gain a better understanding of the Caledonian orogenesis, the origin of the Baltic Shield and the process of land uplift, the static and dynamic properties of the crust and upper mantle are being investigated along a zone which runs from the Norwegian Sea in a south-easterly direction through Sweden, the Bothnian Sea and further into Finland. Geophysical, geodetic and geological studies are being combined along this zone, which has been named the Blue Road Geotraverse. The interdisciplinary study along the Blue Road is an inter-Nordic contribution to international geodynamic research. There follows a number of papers which are concerned with this project.

ISSN:0016-786X    

DOI:10.1080/11035897609454375

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

A greatly generalized section along the Blue Road Geotraverse in Scandinavia is presented. The traverse transects the western part of the Baltic Shield and the Caledonides. Major tectonic features have been indicated according to earlier regional investigations, but some consideration has been given to later research.

ISSN:0016-786X    

DOI:10.1080/11035897609454376

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

Deep-seismic-sounding experiments along the Blue Road Geotraverse were carried out in 1972. Seismic waves from five equally spaced shot points were recorded at altogether 88 recording sites. The seismic project was initiated and plans for the field procedure were made by the Department of Solid Earth Physics at Uppsala. The field measurements were carried out in co-operation with Swedish, German, Norwegian, and Finnish institutes. As the result of a first travel-time interpretation ofP-wave arrivals, velocity models of the lithosphere can be presented.

ISSN:0016-786X    

DOI:10.1080/11035897609454377

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

On the basis of national gravity surveys in Sweden and Norway and additional gravity measurements within a zone ∼50 km wide along the Blue Road Geotraverse, a Bouguer map was produced for the geotraverse area. In order to explain the large, negative, Bouguer anomaly within the mountain area, two-dimensional density models limited by polygons were used, and the geometrical parameters optimized by a least-squares procedure. Mass deficiencies from relicts of a downgoing slab during the Caledonian orogeny seem to be unlikely from the isostatic point of view. Mass deficiencies caused by a depression of the Moho seem reasonable when isostacy is considered. Clear seismic evidence, however, is still lacking.

ISSN:0016-786X    

DOI:10.1080/11035897609454378

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

Ground measurements of the magnetic field were carried out along a 20-km-wide zone along the Blue Road Geotraverse. In addition, a profile of high precision was measured. A large positive anomaly within the mountain area cannot be explained by anomalous magnetization of surface rocks. Optimization of theoretical models shows that it may have its origin at a depth of 30 km, indicating a rise of the Curie isothermal surface from the mountain area to the Baltic shield. The rise of the isotherm may be connected with the land uplift. Interpretation of smaller anomalies reveals the thickness of sedimentary layers.

ISSN:0016-786X    

DOI:10.1080/11035897609454379

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor

摘要:

An attempt is made to synthesize the results of different investigations along the Traverse. For comparison, a map shows the mean values of the topography, the geological cross-section, a seismic-velocity model, the Bouguer field and its interpretation, as well as the magnetic field and a model. The interpretation of seismic-wave travel times does not show a Moho depression below the Caledonides, compared with the Baltic Shield. The interpretation of gravity results by a Moho depression requires a very steep seismic-wave-velocity gradient in the lower crust and almost no velocity jump at the Moho, in order to satisfy the seismic-wave travel times. Because of the difficulty of explaining isostatic compensation of the mountains by such a model, light masses below the lithosphere, such as the relicts of a downgoing slab during the orogeny, should be taken into account to explain both a part of the negative Bouguer field and a part of the isostatic equilibrium.

ISSN:0016-786X    

DOI:10.1080/11035897609454380

出版商:Taylor & Francis Group    

年代:1976

数据来源: Taylor