Marginal basin magmatism in an ancient volcanic arc: Petrology of the Palaeoproterozoic Malå‐group basalts, Skellefte District, northern Sweden

Abstract A new stratigraphic unit, informally called the Mala group, is tentatively suggested for the interval between the arc‐related volcanic Skellefte and Arvidsjaur Groups in the western part of the Skellefte District. The Mala group comprises turbiditic grey wackes and high‐Mg basalts. The basalts vary from sills and lavas in the lower levels to mainly volcaniclastites at the top. The basalts contain characteristic actinolite pseudomorphs after pyroxene. Geochemically the basalts have high contents of Mg, Cr, and Ni and relatively high LIL elements. Tectonic discrimination using trace element geochemistry suggests a volcanicarc setting. The geological setting is interpreted as a marginal basin formed at an advanced stage of the development of the Skellefte extensional continental margin arc. Bergstrom, U., 1997: Marginal basin magmatism in an ancient volcanic arc: Petrology of the Palaeoproterozoic Mala‐group basalts, Skellefte District, northern Sweden. GFF, Vol. 119 (Pt. 2, June), pp. 151–157. Stoc...

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