Early Precambrian basic rocks of the Baltic Shield

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Authors:Brewer, T. S.; Pharaoh, T. C.
Author Affiliations:Primary:
Univ. Nottingham, Nottingham, United Kingdom
Br. Geol. Surv., United Kingdom
Volume Title:Early Precambrian basic magmatism
Volume Authors:Hall, R. P., editor; Hughes, D. J.
Source:Early Precambrian basic magmatism, edited by R. P. Hall and D. J. Hughes, p.273-293. Publisher: Chapman and Hall, New York, NY, United States
Publication Date:1990
Note:In English; illus. incl. sects., chart, geol. sketch maps
Summary:In the broadest of terms, the Baltic Shield developed in the early Proterozoic by sequential accretion to the margins of Archaean continental nuclei. The Archaean terrains were cratonized during the Saamian (3100-2900 m.y.) and Lopian(2000-2600 m.y.) orogenies, subsequent accretion and reworking occurring during the Svecofennian (2000-1750 m.y.), Gothian (1750-1600 m.y.) and Sveconorwegian (250-900 m.y.) orogenies. In recent years the Proterozoic tectonic evolution of the shield has been explained in terms of modern plate tectonic processes. Such models have become even more robust with the recent discovery of ophiolitic relics. There are many strong parallels between the Proterozoic evolution of the Baltic and the Laurentian shields. According to the 'consensus' plate model presented, the majority of the Lapponian and Jatulian supracrustals formed in ensialic rift basins, whereas the Svecofennian development mainly involved subduction processes. Several major problems arise from the model, including: 1) the spatial disposition of the Archaean cratons during the early Proterozoic, 2) the interpretation of arc-type basaltic rocks in the lower Lapponian group on the basis of geochemical signatures, 3) the age of the Karasjok-Kittila belt and significance of the Lapland granulite complex, 4) the degree of tectono-magmatic reprocessing involved in the generation of Svecofennian arc systems and 5) whether or not pre-volcanic Archaean or early Proterozoic crust was involved in the latter. [J.M.H.]
Subjects:Crystalline rocks; Gabbros; IGCP; Igneous rocks; Intrusions; Layered intrusions; Mafic composition; Ophiolite; Petrology; Plutonic rocks; Precambrian; Baltic region; Europe; Fennoscandian Shield; Igneous activity
Abstract Numbers:91M/2101
Record ID:1991002615
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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