摘要:

The earliest recognisable folds (F1) in the Seve nappe in the Åre area in the central Swedish Caledonides include a phase of co-axial refolding (F1Aand F1B). These isoclinal, tight reclined or recumbent folds are parallel to the principal mineral lineation and mylonitic striation. There is a set of tight, reclined folds (F2) which refold the mineral lineation and F1hinges at large angles. The open F3folds refold the F2hinges at small angles. In addition to the above structures, there is also a set of open, upright folds (F1) with axes parallel to the mineral lineation (and to F1) which is younger than F1. The time-relation of these F1folds to the F2folds is not clear. The field evidence indicates that F1Band later folds have developed during different stages of thrusting. The period of migmatization and high-grade metamorphism within the nappe has overlapped with the period of development of the F1and F2structures.

ISSN:0016-786X    

DOI:10.1080/11035897909452564

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035897909452565

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Microstructural and microprobe studies of a staurolite-garnet-sillimanite-biotite schist indicate a peak of metamorphism syntectonic with a third phase of folding in a regional polyphase deformational history. Metamorphic conditions are calculated to be 675 ± 25°C and 500± 25 MPa (5.0± 0.25 kbar) with PH2O = 0.6 Ptot. The implications of such a late peak of metamorphism in this part of the Svecokarelides are assessed.

ISSN:0016-786X    

DOI:10.1080/11035897909452566

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The structure of a small outcrop is compared with the regional structures in the Precambrian of south-eastern Sweden. The peak of deformation is regarded as being later than the oldest plutonics. The major structures are interpreted more in terms of flow and heterogeneous strain than as the result of a process of time-separated, fold interference due to changing stress fields.

ISSN:0016-786X    

DOI:10.1080/11035897909452567

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

An ultrabasic intrusion is described from south-western Värmland, Sweden. It is tentatively inferred to be of Sveconorwegian age. The rock is mainly composed of olivine, which is almost completely altered to serpentine, and secondary minerals, such as amphibole and chlorite. The ultrabasite is suggested to have been tectonically emplaced in its present position.

ISSN:0016-786X    

DOI:10.1080/11035897909452568

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035897909452569

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Radiometric data for igneous rocks, intruding early Proterozoic supracrustals, from two separate areas in north-eastern Sweden are presented. U-Pb analyses on zircons from plutonic rocks of intermediate composition around Lake Paittasjärvi yield an age of 1880 ± 28 Ma. A whole-rock isochron age of 1915± 145 Ma and a plagioclase-hornblendemica age of 1550± 40 Ma are calculated for the same rocks with the Rb-Sr method. Correlated granitoids from the Juoloyanjarvet area, which in part have suffered replacement of plagioclase by scapolite and are intruded by gabbros and younger granites, give a whole-rock Rb-Sr reference line of 1705 Ma and mineral ages of 1535 and 1495 ± 30 Ma. The whole-rock age probably lacks direct geological significance but the mineral ages obtained from both of the above areas may reflect influences from younger plutonism on the dated rocks. One of the intruding gabbros has a Rb-Sr mineral age of 1617 ± 107 Ma. This figure is considered a minimum age of the rock. The impact of scapolitization on the calculated ages is discussed. Decay constants recommended by the IUGS Subcommission on Geochronology (1977) have been used in the calculation of the Rb-Sr and U-Pb ages, which are given at the 95% confidence level.

ISSN:0016-786X    

DOI:10.1080/11035897909452570

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035897909452571

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The large Ragunda intrusion (1320 Ma) and dolerite dykes cutting the intrusion near its western margin have been extensively sampled for palaeomagnetic study. After comprehensive alternating field and thermal demagnetisation, the intrusion yields a mean directionD= 20°,I= 46° (α95= 7°); both polarities are present. Two stages of dyke intrusion are identified from their magnetisations: a small number of dykes have directions similar to the Ragunda intrusion and the remainder yield a meanD= 182°, 7=24° (α95= 14°); both polarities are present in each case and neither dyke suite correlates with the magnetisations of post-Jotnian (ca. 1200 Ma) dolerites from elsewhere in the Fennoscandian Shield. Magnetisations reside in different phases of titanomagnetite, pyrrhotite is a locally important remanence carrier, but maghemite, although sometimes present, has not been identified as a significant carrier. The palaeomagnetic poles help to clarify the form of the apparent polar wander path for the Fennoscandian Shield in Late Proterozoic times.

ISSN:0016-786X    

DOI:10.1080/11035897909452572

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The majority of the reef limestones and associated lithologies of Gotland are weakly magnetised and contain a complex natural remanent magnetisation, but it is established that they contain an Early Palaeozoic, probably Late Silurian, magnetisation. The Earth's magnetic field was predominantly of normal polarity, with the north pole situated near 170°E and 20°N, but it has not been possible to distinguish any occurrence of a field reversal. In addition, a few rocks show anomalous directions, which are interpreted - in conjunction with some Ordovician results - as indicating the presence in Wenlockian times of a steeply inclined NNW-SSE axis of magnetisation.

ISSN:0016-786X    

DOI:10.1080/11035897909452573

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor