Bulletin of the Geological Society of Finland (Jun 1998)
Stratigraphy of the central parts of the Palaeoproterozoic Tampere Schist Belt, southern Finland: review and revision
Abstract
The arc-type Palaeoproterozoic volcanic-sedimentary Tampere Schist Belt (TSB), close to the centre of the Svecofennian Orogen, comprises an E-W-striking major synform in its central parts. This paper presents a review of stratigraphy and proposes a revision of stratigraphic nomenclature of the central TSB. The stratigraphic columns differ from each other in different parts of the belt, and along-strike as well as limb-to-limb correlations are often problematic. However, certain generalizations are possible to make. The pillow-basalt-bearing Haveri formation with EMORB, not arc-type, affinities is the lowermost unit in the northern limb, and it is overlain by the turbidites of the Osara formation. The Haveri formation is regarded as the oldest unit of the TSB and it was evidently related to extension of Palaeoproterozoic crust before ca. 1.91 Ga. The Myllyniemi formation, characterized by mid-fan turbidites, is the lowermost unit in the southern limb. The Myllyniemi turbidites are thought to be broadly coeval with the Osara turbidites, and they were evidently deposited before the emplacement of the 1.904 Ga subaerial dacite- and andesite-rich Koskuenjärvi formation of the northern limb. The turbidites of the Myllyniemi formation and those of the overlying Tuuliniemi formation show a general fining-upward trend. On the other hand, the proportion of arc-type volcanic rocks increases above the Myllyniemi formation and this evolution is accentuated by the growth of the ca. 1.89 Ga Pulesjärvi-Kolunkylä complex of volcanic and sedimentary rocks that was in part subaerial. The subaqueous pyro-/volcaniclastic intermediate rocks among the turbidites of the southern limb possibly contain units coeval with the Koskuenjärvi formation. The 1.889 Ga Takamaa formation, rich in mafic volcanics, was formed after deposition of the sedimentary rocks (e.g. the Veittijärvi conglomerate) of the Pulesjärvi-Kolunkylä complex. The subaerial to shallow-water volcanic and sedimentary rocks of the Tohloppi-Tesoma-Kalkku area, in the southernmost TSB near Tampere, resemble the Pulesjärvi-Kolunkylä complex in age. Their present position gives an impression of a horizon below the Myllyniemi formation, but this is interpreted to be the result of early thrusting. Similarly, the fluvial-deltaic Mauri arenites with a predominantly felsic volcanic provenance are high in the generalized TSB stratigraphic column.
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