The major element geochemistry of the 1.9-1.86 Ga Bergslagen Older Granite Suite, W. Bergslagen, Central Sweden

Abstract

The 1.9-1.86 Ga Bergslagen Older Granite Suite forms part of a co-magmatic series together with a > 10 Km thick sequence of felsic metavolcanics developed in the 3000 km2 of western Bergslagen, Central Sweden. The granites, divided into three geographical groups, are fine to medium grained biotite granites, with field and petrological evidence of high level emplacement, the intrusions cutting their own extrusiva. Postmagmatic hydrothermal alteration has resulted in albitization and variable iron oxidation ratios. Unaltered granite samples are characterized by a high silica content and weak inter-element variations, showing restricted minimum melt compositions. In terms of multicationic classifications the granites belong to an aluminous association, compatible with an origin by anatexis of a felsic to intermediate precursor, with no significant contribution from mafic sources. An origin by anatexis supports current models for a rifted intra-continental or continental margin setting.