Composition of metamorphic rocks and some aspects of evolution of the Lapland Granulite Belt on the Kola Peninsula, USSR

Abstract

Combined geological and petrochemical data suggest that the Lapland Granulite Belt can be divided into a lower sedimentary-volcanic unit and an upper, predominantly sedimentary sequence. Metamorphic rocks from the lower parts of the section have given zircon ages of 2.7 - 2.8 Ga. The geochemical signatures of the metavolcanites and metasedimentary rocks suggest that the Lapland granulites are comparable to Phanerozoic island arc complexes. The composition of the pre-Lopian basement blocks is in agreement with this hypothesis. According to our proposed model, the development of the Belt was initiated by underthrusting of the Belomorian block beneath the Kola block. This led to widespread volcanic activity, which was eventually superseded by the sedimen- tary cycle. The complex was then taken down to depths sufficient for metamor- phic transformations in granulite facies; this occured at around 1.9 - 2.0 Ga.