摘要:

Published data on the initial Sr isotopic composition and range of SiO2content of some representative granites from the Swedish Proterozoic is reviewed. An attempt is made to divide these granites into genetic types related to partial melting of different source materials (igneous or I-type and sedimentary or S-type) and ultimately to the tectonic environment of magma generation. It may thus be possible to distinguish between magmatism initiated entirely within the crust, and magmatism initiated within or at the top of the mantle. Four groups of I-type granitoids can be recognised in the Swedish Proterozoic and these may possibly be related to three phases of subdaction of ocean floor. The second and third subduction phases were separated by a tensional phase possibly related to continental rifting and breakup. Granites of crustal origin can be recognised but are different from S-type granites from the type-area in southeastern Australia, not being depleted in Na and Ca. They were probably generated through the anatexis of Rb-rich volcanics and subordinate continental sediments in two different environments: (a) during regional metamorphism and (b) during regional uplift. This study suggests that both Andinotype and Hercynotype elements are represented in the Swedish Proterozoic and can be distinguished both in space and time. It gives strong encouragement to further critical and open-ended testing of the possibility that plate-tectonic processes were operative in the Proterozoic.

ISSN:0016-786X    

DOI:10.1080/11035898009450896

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

The Presvecokarelian (Archean) basement of Finland consists mainly of granitoids and granite gneisses. Locally, there also occur some greenstone provinces, where komatiites occur as minor but characteristic rocks. The Karelian formations (Upper Archean-Lower Proterozoic) lie discordantly over the Presvecokarelian basement and are at least 2500 Ma old. The Karelian formations are divisible into Sariolian, Jatulian and Kalevian groups and the former two further into Lower, Middle and Upper subgroups. The boundary between the Sariolian and the Jatulian group is estimated to be ca. 2300 Ma old and the one between the Jatulian and the Kalevian ca. 2000 Ma old. Significant key horizons of the Karelian formations are Upper Jatulian dolomites, black schísts and volcanites, with an age of ca. 2100–2000 Ma, and a thick orthoquartzite with overlying and underlying volcanites. The synorogenic granitoids cutting the Kalevian metasediments are ca. 1900 Ma old and cogenetic with the metavolcanites overlying Svecofennian phyllites and mica schísts.

ISSN:0016-786X    

DOI:10.1080/11035898009450897

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

Domes of presumed basement (> 2500 Ma) appear near Luleå, southeastern Norrbotten, northern Sweden. The stratigraphy of this area is briefly described and a tentative outline of the general geology around the Gulf of Bothnia is given, stressing the importance of block faulting for the present distribution of geological units.

ISSN:0016-786X    

DOI:10.1080/11035898009450898

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450899

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450900

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450902

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450904

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450905

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450907

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898009450909

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor