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The Kostomuksha greenstone belt, NW Baltic Shield: remnant of a late Archaean oceanic plateau?
Author(s) -
Puchtel I. S.,
Hofmann A. W.,
Jochum K. P.,
Mezger K.,
Shchipansky A. A.,
Samsonov A. V.
Publication year - 1997
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/j.1365-3121.1997.tb00009.x
Subject(s) - geology , greenstone belt , archean , baltic shield , plateau (mathematics) , shield , geochemistry , geomorphology , petrology , crust , mathematical analysis , mathematics
The Kostomuksha greenstone belt consists of two lithotectonic terranes, one mafic igneous and the other sedimentary, separated by a major shear zone. The former contains submarine 2.8 Gyr old komatiite‐basalt lavas and volcaniclastic lithologies with trace element and isotopic compositions resembling those of recent oceanic flood basalts [ɛNd(T) =+ 2,8, μ. 1 = 8.73 (Nb/Th) N = 1.5–2.1 (Nb/La) N = 1.0–1.5]. We suggest that the mafic terrane is a remnant of the upper crustal part of an Archaean oceanic plateau derived from partial melting of a mantle plume head. When the plateau reached the continental margin, it collided with the sedimentary terrane but was too buoyant to subduct. As a result, the volcanic section of the plateau was imbricated and obducted thus becoming a new piece of continental crust. The deeper zones were subducted and disappeared from the geological record.