摘要:

Three samples of broken Svecokarelian granodioritic bedrock from the centre of the Söderfjärden crater resemble tuffaceous breccias in appearance and yield age values of 1238 ± 18, 1321 ± 19, and 1321 ± 19 Ma by the40K-40Ar whole-rock method. However, the Lower Cambrian sedimentary infill of the crater dates it at about 550 Ma. The mineralogical shock-like deformation effects in the breccia are limited to formation of planar elements in quartz and devitrification of plagioclase. The cratering explosion seems to have left the radiogenic40Ar partially un-degassed in the potassium minerals. This factor does not conflict essentially with the earlier interpretation, favoured by the author, that the Söderfjärden crater was formed by a cryptovolcanic explosion. However, the alternative mode of formation, i.e. meteorite impact, is now a more probable explanation for the origin of the crater.

ISSN:0016-786X    

DOI:10.1080/11035898509452604

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

A Rb-Sr whole rock isochron for the Finspång augen gneiss, south central Sweden, yields an age of 1834 ± 21 Ma which is compared with intrusive ages for similar rocks in the neighbourhood. The augen gneiss is interpreted as an outer ‘skin’ surrounding younger granite intrusions.

ISSN:0016-786X    

DOI:10.1080/11035898509452605

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Potassium/rubidium ratios of the granitoids (mainly granodiorites) of the Svecokarelidic (1.8–1.9 Ga) Rautio batholith in western Finland are reported in order to evaluate the use of the ratio as an indicator of the porphyry-type Mo-Cu mineralizations associated with the batholithic rocks. The results show that, in spite of the occurrence of several minor Mo-Cu mineralizations within the batholith, the K/Rb ratios are not lowered to the values reported as critical for mineralization in granitic rocks. It is therefore concluded that the criteria of ore-bearing potential applied to granites are not applicable in batholiths which are mainly granodioritic.

ISSN:0016-786X    

DOI:10.1080/11035898509452606

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509452607

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

This palaeomagnetic investigation comprises basic rocks from six localities from the Svecokarelian zone in northern Sweden. Most of the pole positions in this study and other reported poles of Svecokarelian and post-Svecokarelian rocks fall within an approximately 12 degrees wide band running from east to west representing ages of magnetizations from 1880-1700 to ∼ 1530 Ma. Thermal demagnetizations of specimens of the probably oldest massifs indicate a possible backward continuation of the polar wandering path. Mineralogical studies of thin sections of the rocks show ore symplectites and myrmekitic textures indicating a slow rate of cooling at least at the end of the rock formation. Signs of metamorphism are demonstrated by the existence of secondary minerals, including magnetite, not related to late magmatic alterations. The distribution of site means as well as the change of directions of the remanence vectors during thermal demagnetization can be explained by a slow rate of cooling and where signs of metamorphism exist by partial remagnetization of the rock. This study has, apart from the palaeomagnetic results, demonstrated the difficulty of correlating radiometric ages with ages of magnetization.

ISSN:0016-786X    

DOI:10.1080/11035898509452608

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898509452609

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The Breven dolerite dike in the eastern part of south central Sweden has been remapped. A large central part of the dike is occupied by a red granophyre, most probably a late differentiate of the dolerite. To the east of the major dike there is a hybrid dolerite-breccia with xenoliths of granophyre showing different stages of assimilation. The latter dike has a width of around 100 m and a length of at least 8 km. These observations suggest several pulses of dolerite in the dike system.

ISSN:0016-786X    

DOI:10.1080/11035898509452610

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

One of the gabbroid intrusions of the Svecokarelian of central Sweden, the Kramsta gabbro, has been investigated concerning mineral compositions along an intersecting drill-core. Several cores have been drilled through the gabbro. The analysed core was considered to be representative. A cryptic layering is displayed by the clino- and orthopyroxenes, as well as the amphiboles, all revealing increase of MgO/FeO + MgO with increasing depth. The V-content of ilmenite and magnetite increases in the same way. The lamination of plagioclase suggests igneous layering in the rock body. All these observations indicate accordance between primary and present orientation in respect of ‘way up’. Further, the existing rock body seems to constitute only a subordinate part of the primary one. Igneous layering may explain the accumulation of V-rich magnetite. The cryptic layering will help to locate such layers, which have potential value as ores.

ISSN:0016-786X    

DOI:10.1080/11035898509452611

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Microhardness, reflectance and unit cell length have been measured on pyrites associated with Swedish base metal ores. From statistical appraisal of their physical and dimensional properties, it is shown that, on the basis of unit cell length, two distinct pyrite groups exist: those from central and southern Sweden and those from Västerbotten and Norrbotten in northern Sweden. Within the Caledonian Region the hardness of the pyrites can be correlated with grade of metamorphism.

ISSN:0016-786X    

DOI:10.1080/11035898509452612

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The Siljan structure represents a deep erosion level of an astrobleme. Post-impact formation of minerals as various types of vein fillings is common. Non-shocked milky quartz from a large vein revealed fluid inclusions of three types:(1) one-phase, regularly shaped inclusions, < 1 to 10 μm in size, (2) two-phase, regularly to irregularly shaped inclusions, 2 to 7 μm, (3) larger irregular two-phase inclusions, 8–20 μm. The one-phase inclusions dominate; density of inclusion occurrence is estimated at 46 × 104inclusions per cm2. Melting temperatures indicate a total salinity of 1.0 eq. wt. % NaCl. Homogenization temperatures range between 165 and 309°C. The fluid inclusion data imply a complex origin of the quartz. It consists in part of breccia fragments formed after the impact. The quartz vein was cemented by deep circulating meteoric waters at successively lowered temperatures initially over 300°C.

ISSN:0016-786X    

DOI:10.1080/11035898509452613

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor