摘要:

A seismic refraction profile about 34 km long was investigated in the Tåsjön area of north central Sweden. The profile was orientated nearly perpendicular to the Caledonian Front. Very clear first arrivals were recorded from the sedimentary layers, as well as from the underlying granitic basement. From some of the shot points, transverse waves were recorded, as well as surface waves. The interpretation has been made, using travel-time analysis of the firstP-wave arrivals, as well asS-wave arrivals. Relatively high velocities, 4.4–5.4 km/s were recorded from the sedimentary cover. A normal upper-crust velocity, about 6.0 km/s, was recorded from the basement. The thickness of the sedimentary cover increases from about 0.34 km in the eastern part of the profile to about 1.3 km in the western part of the profile. The granitic basement rises from 0.94 km below sea level in the western part of the Caledonian Front to 0.09 km below sea level in the central part of the Front.

ISSN:0016-786X    

DOI:10.1080/11035898009450842

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A small outcrop of massive Sudbury-type mineralization has recently been exposed by roadworkers at Notträsk in northeastern Sweden. Two pentlandite types occur:type A, as large irregular patches between pyrrhotite grains with well-developed octahedral partings andtype B, as flames in pyrrhotite. The type A pentlandite has a composition approximating Ni4.2Fe3.9Co0.9S8and the type B contains less cobalt, Ni4.2Fe4.1Co0.7S8. Type A pentlandite is altered to violarite with a composition Ni1.5Fe1.2Co0.3S4to Ni1.5Fe1.1Co0.4S4. Violarite formation occurs through the reaction Ni4.3Fe3.9Co0.8S8→. 2Ni1.5Fe1.1Co0.4S4+1.3Ni2++2.7Fe2+. This results in a decrease in the Fe:Ni ratio of the co-existing violarite and indicates that cobalt behaves conservatively. Pentlandite-A formed below 300°C from the monosulfide solid solution, whereas pentlandite-B formed at even lower temperatures by late-stage readjustments in the Notträsk mineral assemblage.

ISSN:0016-786X    

DOI:10.1080/11035898009450843

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Analysis of seismicity data for Fennoscandia for 1954–1978 has resulted in a comprehensive catalogue of 604 earthquakes, most of which with locations based on instrumental recordings. Detailed analysis of four well-recorded earthquakes near the NORSAR array has given very accurate focal depth estimates of 6,22,23 and 31 km, as well as one normal and two oblique-slip fault plane solutions. These and some other local events have been used for the construction of a crustal model for southeastern Norway. A short description is given of the outstanding 1978 Meløy earthquake sequence in northern Norway, where about 10 000 microearthquakes were recorded over only 10 weeks. The seismicity in the Oslo Graben area is taken to indicate that this is a general zone of weakness, with local geological conditions strongly influencing the focal mechanisms. There is increasing evidence suggesting that global tectonic movements are a key factor for the accumulation of regional stress in Fennoscandia.

ISSN:0016-786X    

DOI:10.1080/11035898009450844

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450845

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Structural and metamorphic discontinuities in the Tømmerås basement-cover sequence confirm the allochthonous character of the Lower Snåsa Group, the Leksdalsvann Group, and the upper basement of the Tømmerås Window. Three major deformational events are recognized. During an early event the upper unit (the Snåsa Group amphibolites and gneisses) was metamorphosed under amphibolite facies conditions and thereafter became emplaced above the unmetamorphosed Leksdalsvann sediments. The interkinematic (D1-D2) parageneses of these sediments indicate a highPH2OandTca. 450°C. D2 recrystallization, corresponding to the transitional greenschist-amphibolite facies (500–550°C,P> 600 MPa), is largely controlled by the distribution of shear strain. Calcium-rich mantles of late D2 garnets in the same sediments indicate a pressure peak before the main thrusting (late D2). D3 folded the thrusts and the isograd pattern established during D2 around the NE-SW trending axis of the Tømmerås Antiform. Various features indicate the subordinate role of Caledonization in the Tømmerås ‘autochthon’: the decrease of grade with increasing tectono-stratigraphic depth, the open megastructures and the mylonites and localPT-peaks. This is noteworthy because Tømmerås is located on the very border of the coastal gneiss region, an area previously supposed to have been subject to Caledonian mobilization.

ISSN:0016-786X    

DOI:10.1080/11035898009450846

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Two granites in western Troms (Ersfjord granite and Rødberg granite), previously thought to be Caledonian intrusives, have been dated by the Rb-Sr whole rock method. A seven-point Rb-Sr isochron age of 1706±15 Ma and an initial87Sr/86Sr ratio of 0.70404±0.00034 (1[sgrave]) was obtained on the Ersfjord granite. An isochron plot of seven samples from the Rødberg granite failed to define an isochron age, but also suggests a Precambrian age for this intrusive. On the basis of these ages it is concluded that no deep-seated reactivation of the Precambrian basement took place in western Troms during the Caledonian orogeny. The ages obtained correlate with the latest episode of mangerite intrusion in the Lofoten-Vesterålen area and with the late syn- and post-kinematic Svecokarelian granites in northern Sweden.

ISSN:0016-786X    

DOI:10.1080/11035898009450847

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Intermediate and acid volcanic rocks from the Öræfajökull central volcano, southeast Iceland, are hybrids with calc-alkaline affinity. These rocks are characterized by basic xenocrysts of olivine, plagioclase, and clinopyroxene set in a glassy matrix. Linear variation curves for a number of major and trace elements show that the rocks are mixing products of basic and silicic members of the main series of the volcano. It is concluded that this mixing results from contamination of silicic melts by basaltic and gabbroic xenoliths.

ISSN:0016-786X    

DOI:10.1080/11035898009450848

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450849

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Radiometric ages published 1960–1979 for Swedish rocks and minerals have been tabulated and, when appropriate, recalculated with the new recommended decay constants (R. H. Steiper & E. Jäger, 1977: Convention on the use of decay constants in geo- and cosmochronology.Earth and Planetary Science Letters 36, 359–362).

ISSN:0016-786X    

DOI:10.1080/11035898009450850

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The western part of the Bothnian Bay (northern Gulf of Bothnia) has been investigated by means of seismic reflection and refraction measurements. The sea floor was found to consist largely of glacial drift. The postglacial sediments are unevenly distributed with a dominance in the deeper basins. Till accumulations form an abundance of distinctly separated irregular beds. The upper till beds are provisionally attributed to the Weichselian glaciation whereas the lower beds are regarded as pre-Weichselian. The crystalline bedrock of the Bothnian Bay is to a great extent covered by sedimentary rocks of the Upper Riphean Muhos formation. In the central parts of the Bay, the Muhos rocks are succeeded by almost 100 m of sedimentary rocks which structurally closely resemble the Lower Cambrian stratal sequence of the Bothnian Sea.

ISSN:0016-786X    

DOI:10.1080/11035898009450851

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor