摘要:

In south-western Sweden, two areas separated by a major tectonic zone were selected for study of the earliest known granitoid groups. This was done in a recently mapped region. In both reference areas, the early granitoids, now dominantly gneissic, comprise the majority of rocks by volume. The western granitoid group is cale-alkaline, with granodiorites being predominant. The eastern granitoid group is distinetly more acid and potassium-rich. The chemical trend is cale-alkaline with alkali-calcie inclination. The niggli ratio of qz vs. si and also the Sr/CaO ratio differ between the two rock groups, the latter being highest in the eastern group. The granitoids have intruded supracrustals of intermediary composition in the western region. In the eastern region, the side-rocks are scattered amphibolites and a few xenoliths of supracrustal gneisses. The western granitoids thus intruded into a sial crust, while the eastern granitoids apparently display a more paradoxical situation: intrusion into a dominantly basic crust by granitoids which are rather evolved. The latter aspect seems to indicate either that the sial crust was assimilated, which is not supported by field evidence,orthat the differentiation process was prolonged. The latter interpretation seems to be supported by the higher Sr/CaO ratio for the eastern granitoid group, which indicates an intermediary or greater (>40 km) depth of magma formation.

ISSN:0016-786X    

DOI:10.1080/11035898509452620

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The type material ofHalkieria obliquaPoulsen 1967 from the Lower Cambrian ‘Grønne Skifre’(‘Green Shales’) of Bornholm, Denmark, is redescribed.H. obliquais the type species ofHalkieriaPoulsen 1967, originally described as a probable hyolith, but now interpreted to represent the Lower and Middle Cambrian Sachitida He 1980, a widespread group of lepidote metazoans of problematic affinities. The order contains the families Wiwaxiidae Walcott 1911 and Halkieriidae Poulsen 1967. The type material of H.obliquaconsists of six cultrate sclerites. It is not known whetherH. obliquaalso carried palmate and spiniform sclerites. The type and only specimen ofH. symmetricaPoulsen 1967 is the counterpart of the figured paratype ofH. obliqua;the two species names are considered to be synonyms, andH. obliquais selected as the valid name.

ISSN:0016-786X    

DOI:10.1080/11035898509452621

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Data on the contents of 29 major, minor and trace elements in MAG-1 are given and are discussed with reference to litterature values.

ISSN:0016-786X    

DOI:10.1080/11035898509452622

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The differentiated, sulfide-bearing gabbro near the city of Boden in northern Sweden has been investigated in order to get a plausible model for its formation, shape and age. The gabbro is associated with a major fault system along which several intrusive bodies occur. The largest of these has been traversed by a gravimetric, magnetometric and geological profile. The investigated intrusion is undeformed and oval-shaped and covers some 20 km2. The outer parts of the body consist of a norite in contact with older meatasediments and granites of varying age. Inside the norite occurs a magnetite-rich gabbro, which forms a ring around the centre of the massif, which in turn consists of leucogabbro-olivine gabbro. Fe, Ti and K are low in the centre where Mg and Cr have their highest contents. Impregnations of sulfides and a massive pyrrhotite vein with some 1 % Ni are located in the norite. A number of intrusion models have been tested by computer modelling combining gravimetric and magnetic field data. The most probable model seems to be a funnel-shaped body pointing downwards. The different gabbro types dip steeply inwards indicating vertical zones rather than horizontal. Palaeomagnetic measurements show that the intrusion has a similar orientation of magnetization as other gabbros of the Haparanda series in northern Sweden (1800–1900 Ga, Rb-Sr). Furthermore, the pole distributions show that the rock cooled slowly, which may indicate that the present outcrop is a deep part of an eroded intrusion. The massif is supposed to have been formed by a diapiric re-emplacement of primary horizontal cumulates formed in the sequence olivine gabbro-leucogabbro-magnetite-bearing gabbro-norite.

ISSN:0016-786X    

DOI:10.1080/11035898509452623

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Rb-Sr whole rock dating of veins and their aureoles from the postorogenic Svecokarelian Rätan granite, central Sweden, yields an isochron age of 1596 ± 21 Ma and an initial87Sr/56Sr ratio of 0.7046 ± 0.0014. A comparison with published data, after recalculation, suggests that the postorogenic magmatic activity was accompanied by block movements and burial metamorphism. There was also a shifting of the magmatic activity from the Rätan area towards southwest over Ålvdalen into Norway.

ISSN:0016-786X    

DOI:10.1080/11035898509452624

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Primary textures in the Kiirunavaara apatite iron ore suggest a magmatic origin. They comprise (a) columnar development of magnetite similar to a crystal growth texture due to rapid cooling in the El Laco iron ore, Chile, (b) ‘skeleton ore’ with platy magnetite, locally dendritic - a widespread ore type also in the other iron deposits of the Kiruna Field, and (c) ore with thin tabular pyroxene crystals, partly dendritic, distributed in a way clearly indicating flow in a consolidating ‘ore magma’. In addition, the reported cross-bedding and graded bedding in the Kiruna ores might be igneous sedimentation features. The relationship between different ore types suggests a complex emplacement history. Some associated breccias and ‘conglomerates’ might be the consequence of gas discharge, i.e. tuffisites. Some of the Kiruna ores appear to have a carbonatitic affinity, with ankerite as a seemingly primary constituent; certain associated albite-rich rocks might be regarded as analogous to fenites. The inferred ensialic rift setting of the volcanic country rock is consistent with this interpretation.

ISSN:0016-786X    

DOI:10.1080/11035898509452625

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509452626

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A case of iron precipitation in glaciofluvial material from Lake Hämeenjärvi near Oulu, northern Finland is described. Special emphasis is placed on the elucidation of the geochemical regime, the Eh-pH conditions and the chemical composition of the groundwater and the precipitate. In the case studied, deposition of iron is a result of a rise of Eh from + 400 mV to + 560 mV at the top of the watertable. On an Eh-pH equilibrium diagram the process, however, operates entirely within the field specified theoretically for ferric hydroxide. The total annual rate of deposition has been calculated to be about 15 g Fe/m2on the basis of an average annual rate of flow of 5 1 water/s in a discharge creek. The texture of the precipitate and the distribution of Fe, Mn, Si and Al in it have been studied using scanning electron microscope and EDS. X-ray diffractometry, TGA and DTA studies show that the precipitate is in an amorphous state and contains 17.90% water expelled below 880°C.

ISSN:0016-786X    

DOI:10.1080/11035898509452627

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Radiometric dating of the red, medium- to coarse-grained Vånga granite, south Sweden, gives a spectrum of ages depending on method and material. The granite is referred to the Karlshamn group of rocks and is believed to have formed, after the crystallization of the Karlshamn granite, from residual liquids contaminated with foreign material. The Vånga granite was emplaced ca. 1350 Ma ago and was later intruded by fine-grained granite dikes, in connection with activity in the Protogine zone around 1200 Ma ago.

ISSN:0016-786X    

DOI:10.1080/11035898509452628

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509452629

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor