摘要:

K-Ar analyses of 20 hornblendes from skarns and associated metabasites in the Hjulsjö area of the Bergslagen ore province, central Sweden, define an age of 1.83 ± 0.05 Ga. This age is interpreted in terms of the geological relationships as signalling a period of skarn-formation and metamorphism along with episodes of shearing and basic dike intrusion. Following the hypothesis that the skarn ores were formed by sea-floor hydrothermal metamorphism, this age should also be attributed to the deposition of the enclosing volcano-sedimentary leptite-hälleflinta sequence and the injection and extrusion of basic magma. Analyses of 13 biotites from the skarns and enclosing metavolcanic leptites produce K-Ar and Rb-Sr ages of 1.69 ± 0.05 Ga and 1.65 ± 0.04 Ga, respectively; these are related to an episode of mild crustal heating associated with nearby post-orogenic granite intrusions dated at 1.70 Ga.

ISSN:0016-786X    

DOI:10.1080/11035898209454526

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209454527

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Two generations of Sveconorwegian granitoid rocks are recognized in the Orust-Skaftölandet sector of the Stora Le-Marstrand belt of SW Sweden. The earlier is a suite of large pegmatites containing quartz, plagioclase, K-feldspar, muscovite, minor biotite and garnet. These bodies cut the D3-deformed Orust dykes which have a metamorphic age of 1060 Ma. They are in turn deformed by F4 folds. Rb-Sr ages calculated from three mineral pairs from two of these pegmatite bodies arc close to a mean value of 950 Ma which is interpreted as the emplacement age of the pegmatites. The later generation of Sveconorwegian granitoid is represented by the 891 Ma Bohus granite pluton and associated minor pegmatites. In the islands west of Skaftölandet the Bohus granite contact clearly cuts the Orust dykes and also elements of the post-dyke (Sveconorwegian) deformations, D3 and D4 (and probably D6). The granite contact itself is undeformed although the granite elsewhere exhibits minor shears. These granitoid ages place close constraints on the timing of Sveconorwegian deformations in this area.

ISSN:0016-786X    

DOI:10.1080/11035898209454528

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209454529

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The Sundsta granite is a reddish acidic granite, situated in the Western Pregothian mega-unit in Värmland, south-western Sweden. Its Rb-Sr whole-rock age is 1566 ±39 Ma with an initial ratio of 0.705 ±0.003. The region is dominated by grey, migmatized granitoids presumably belonging to the Åmål-I group which has ages of 1650–1700 Ma. The marked difference in degree of migmatization between these two rock-units may indicate that the intrusion of the Sundsta granite post-dates the main migmatization phase of the Åmål-I granitoid in this region.

ISSN:0016-786X    

DOI:10.1080/11035898209454530

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209454531

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The Gevsjön Formation (calcareous phyllite — garbenschiefer) of the Tännforsfältet Köli is divided into three tectonic units, separated by two important mylonite zones. These mylonite zones exhibit an earlier ductile phase of deformation and a later brittle phase with brecciation of the mylonitic foliation. Associated with this brecciation pseudotachylites have been recognized at four localities. A fifth locality is so far not directly related to any mylonite zone, but occurs close below the upper mylonite zone. The change from mylonite formation (ductile deformation) to the development of breccias and pseudotachylites represents a change in physical conditions during translation of the nappes. Early movement occurred at higher and the later movement at lower temperatures, implying that the thrusting involved progressive translation of the Köli Nappes to higher structural levels.

ISSN:0016-786X    

DOI:10.1080/11035898209454532

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Mineral graded rhythmic layering occurs throughout most of the Fongen—Hyllingen basic complex. Non-cumulate, fine-grained, granular rocks are found as a conformal part of the layered gabbros. In one particular locality isomodal coarse-grained layered structures are developed within these non-cumulate granular rocks. These layers range mineralogically from olivine + Ca-rich pyroxene + Ca-poor pyroxene + plagioclase to amphibole + Ca-poor pyroxene + plagioclase. The sudden appearance of high concentrations of amphibole, without indications of amphibole primocrysts in the surrounding granular rocks or in adjacent normal rhythmically layered gabbro, is difficult to interpret in the light of the conventional cumulate theory. Heterogeneous nucleation and growth close to or on the bottom of the magma chamber is preferred for the origin of the layered structures.

ISSN:0016-786X    

DOI:10.1080/11035898209454533

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Magnetite and sphalerite in the non-apatitic iron ores and sulphide ores of central Sweden, which are considered to be of volcanogene, syngenetic origin, have been investigated chemically. Microprobe analyses show a pure magnetite, which besides iron, only contains small amounts of additional elements. This concerns also magnetite occurring in iron ore deposits with magnesia-rich alterations, previously attributed to a pyrometasomatic origin, but here considered as para-contemporaneous with the volcanism. The uniform composition of magnetite points to a common source of the iron in the different types of ore. The small contents of manganese (around 1 wt% MnO) in the magnetite of the manganiferous skarn iron ores are due to a higher manganese activity in the ore-bearing solutions. The iron content of sphalerite in the manganiferous skarn iron ores and the sulphide ores varies between 12.8 and 18.6 mole % FeS. The sphalerite in the manganiferous skarn iron ores contains up to 2 wt % Mn. The variations in the iron and manganese contents of the sphalerite are attributed to primary compositional variations during the formation.

ISSN:0016-786X    

DOI:10.1080/11035898209454534

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The thermal conductivities of 13 rock units of Precambrian, Palaeozoic and Mesozoic age on the island of Bornholm (Denmark) have been measured in situ by the cylindrical thermal conductivity probe technique. Results from the individual Precambrian rocks show narrow distributions with an overall range of 2.4–3.8 W/(m K). As a comparison with theoretical predictions based on mineral compositions indicates accordance within reasonable limits of accuracy, the measured thermal conductivities are considered to be representative for the rocks in question. In contrast to the Precambrian crystalline rocks the younger sedimentary rocks show a wider range of thermal conductivities (1.2–6.2 W/(mK)). In addition to the presentation of results, some special field conditions are considered.

ISSN:0016-786X    

DOI:10.1080/11035898209454535

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor