A plate tectonic interpretation of the Precambrian of the Archipelago of southwestern Finland

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Authors:Edelman, N.; Jaanus-Jarkkala, M.
Author Affiliations:Primary:
Abo Akad., Abo 20500, Finland
Source:Bulletin - Geological Survey of Finland, Vol.325, 33p. Publisher: Geologian Tutkimuskeskus, Espoo, Finland. ISSN: 0367-522X
Publication Date:1983
Note:In English. 38 refs.
Summary:Stratigraphically and tectonically the region is divided into four zones, the northern, central and southern zones (NZ, CZ and SZ) and the iron ore zone. In the SZ there is a strongly deformed and banded formation now interpreted as a melange along a subduction zone. Along the melange zone a southern plate was subducted under a northern one. The southern plate carried a continental source area for sediments which were deposited in a northerly deepening basin. The melange was formed through the intermingling of silts with volcanic material and ultramafic slabs from the oceanic crust. In the CZ sedimentation began with shallow-water silt deposition followed by the development of a volcanic island arc with limestone reefs. Finally, the area subsided and deep water sedimentation proceeded with greywackes and clays. In the NZ the sea remained deep during the whole evolution. From the deeper section of the subduction zone magmas rose and produced the volcanoes of the CV and NZ (with associated gabbros). The advance of the southern plate caused folding in the supracrustal rocks, the intensity of folding and deformation decreasing northwards from the subduction zone, and gabbro-granodiorite magmas were intruded as lenses in the supracrustal rocks. Then basic magmas rose along joints in the brittle rocks, forming amphibolite dykes. Later, the fractured area offered a convenient pathway for post-orogenic diabase and granite intrusive rocks. Granite domes rose on both sides of the subduction zone, suggesting once again that the southern plate was subducted under the northern one since the granitic intrusions to the north are larger than those to the south. However, in the area around Noto, a fan of lens-shaped magnetic anomalies suggests that some slices of the southern continent appear to have formed over the northern plate in that area. [J.M.H.]
Subjects:Gabbros; Igneous rocks; Melange; Petrology; Plate tectonics; Plutonic rocks; Precambrian; Proterozoic; Stratigraphy; Subduction; Tectonophysics; Ultramafics; Upper Precambrian; Europe; Finland; Scandinavia; Western Europe; Southwestern Finland
Coordinates:N595800 N604500 E0220000 E0202000
Abstract Numbers:85M/1937
Record ID:1986020563
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from PASCAL, Institute de l'Information Scientifique et Technique
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