摘要:

The spectral ratio technique of Phinney, R. A., 1964: Structure of the earth's crust from spectral behavior of long period body waves (Journal of Geophysical Research 69, 29973017) has been used for estimating crustal thickness beneath 11 Fennoscandian seismograph stations equipped with three-component long period instruments. Extended areas of Mono depths of the order of 45 km were found in the northeastern parts of Fennoscandia with a local maximum of 47 km in the Bothnian Bay (northern Gulf of Bothnia). The coastal areas of southeastern Norway and Zealand (Denmark) exhibit crustal thicknesses in the range 28–33 km. These results agree well with those obtained from conventional seismic profiling when the length of the profile is 300 km or more. A comparison between our results and other geophysical data gives that the oldest provinces exhibit the thickest crust and the lowest heat-flow rate as well. The correlation between Moho depths and geophysical parameters such as post-glacial uplift and gravity anomalies appears at best to be poor.

ISSN:0016-786X    

DOI:10.1080/11035898109455196

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The plutonic rocks, sövite ring dykes and alnöite dykes belonging to the (Cambrian) Alnön Complex have been analysed for palaeomagnetic study. Total NRM's residing in magnetite and pyrrhotite are locally very high in the plutonic facies and variable in the sövite dykes; all the alkaline phases have NRM's dominated by low coercivity components. Alternating field demagnetisation isolates a range of remanence directions, but a principal mean ofD= 107°,I= 2°(α95= 9°) in the bulk of the sövite and alnöite dykes is defined by both polarities and confirmed by thermal cleaning. A subsidiary direction ofD=350°,I= 15° (α95= 11°) is recognised predominantly in the plutonic rocks. The data contribute to the sparse Cambrian palaeomagnetic record from the Fennoscandian Shield and support earlier suggestions of large apparent polar wander motion in Cambrian times.

ISSN:0016-786X    

DOI:10.1080/11035898109455197

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898109455198

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

A zircon study has been made on folded, conformable gneisses and an intrusive igneous rock from the northeastern part of Sweden. U-Pb ages of size and colour fractions of zircon concentrates from the gneisses show complex distributions on the concordia plot. This is related to varying degrees of secondary overgrowth on zircon cores and the formation of new zircons during the Svecokarelian (early Proterozoic) orogeny. Detrital zircons from a very pure quartzite have a maximum age of about 2700 Ma. They almost completely lack overgrowth textures and indicate an age close to that of the Archaean, conceivably igneous, source material. Zircons from the mica and amphibole gneisses have subhedral and rounded cores which, together with the observed layering, imply a sedimentary origin. They have apparent ages of less than 2063 Ma and close to the main metamorphic event, about 1850 Ma ago. Because of the low overgrowth/core volume ratios observed, one may suspect that the zircon core material in the mica and amphibole gneisses was in part derived from Proterozoic volcanic rocks. Thus, the recorded zircon ages favour Proterozoic deposition for all para-gneisses investigated, which is not consistent with other recent investigations. The minimum age of deposition is marked by an intrusive, foliated granodiorite with an age of 1873 ± 23 Ma (2 δ).

ISSN:0016-786X    

DOI:10.1080/11035898109455199

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

The eleven currently available (May 1980) source mechanisms of Fennoscandian earthquakes are analysed. The orientations of the horizontal stresses involved in the faulting are estimated from the fault solutions. The NW-SE orientation of the largest horizontal compression found in a large number of various investigations in continental Europe north of the Alps, is confirmed by the eleven source mechanisms. This result is shown to be statistically significant. The dominating type of faulting is strike-slip on close to vertical fault planes. The agreement between these earthquakes and the European regional stress field strongly suggests that the Fennoscandian earthquakes are related to tectonic forces.

ISSN:0016-786X    

DOI:10.1080/11035898109455200

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898109455201

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

A fold interference pattern based on preserved macrostructures (inter-related supracrustal and infracrustal rocks of different competencies) has been investigated. By means of these structures it has been possible to reconstruct the main folds and to unravel the tectonic evolution of the area. The oldest plutonic rocks were probably intruded and solidified prior to major deformations. A combination of a horizontal, regionally directed stress from east to west and north-south compressions caused by secondary stresses from irregularly distributed, tectonically competent plutonic bodies gave rise to the present structures and fold interference pattern of the region (isoclinal folding F1, and cross-folding F2). Already the first phase of deformation involved pegmatites and probably took place under high-grade metamorphism and low viscosity during a late stage of the orogenic evolution. At present there is little evidence that the main structures of the region were formed due to the diapiric rise of the old plutonic rocks. On the contrary, regional compression seems to be the primary cause of deformation, the intrusives mainly acting in a passive way.

ISSN:0016-786X    

DOI:10.1080/11035898109455202

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Felix Tegengren passed away in March 1980. He was a well known international expert on mining geology and author of diverse major synopses on ore deposits. A short review of his long active life is given, followed by a list of his publications.

ISSN:0016-786X    

DOI:10.1080/11035898109455203

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

摘要:

Stichocystisis re-described. The genus is a rhombiferan with exothecal pore structures developed in a rhomb-in-rhomb pattern with canals embedded within narrow calcite ridges. The pore system developed by regular addition of new sutural pores which later in ontogeny became separated by a calcite ridge as the canal grew outwards from the suture. This type of pore structure is highly specialized. The plate configuration of the oral-anal area clearly putsStichocystisamongst the Caryocystitidae and close to the generaHeliocrinitesandLophotocystiswith which it shares many characteristics. The two orders of the Rhombifera, the Dichoporita and the Fistuliporita reflect two fundamentally different types of pore structures, endothecal and exothecal. With regard to these structures, the order Fistuliporita is more closely related to the Class Diploporita than to the Dichoporita.

ISSN:0016-786X    

DOI:10.1080/11035898109455204

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898109455205

出版商:Taylor & Francis Group    

年代:1981

数据来源: Taylor