Chronology of Proterozoic orogenic processes at the Archaean continental margin in northern Sweden

• The Proterozoic Svecofennian orogeny was characterized by the rapid formation of great amounts of juvenile continental crust and extensive remobilization of older crust. This paper considers U---Pb zircon ages and some geochemical and lithostratigraphic features of the Svecofennian in the continental-margin area between the Skellefte ore district and the boundary of the Archaean craton farther north in Sweden. New U---Pb zircon ages constrain the igneous activity of Svecofennian crust formation in northern Sweden to between 1930 and 1870 Ma ago. The same time constraints apply also to crust formation farther east in Finland. Orogeny along the entire Archaean-Proterozoic boundary zone was thus simultaneous and does not represent an east-to-west event succession. It is argued that rocks with similar major element compositions but distinctly different trace element characteristics were formed simultaneously but in different plate-tectonic environments. By ≈ 1875 Ma ago, the Svecofennian volcanic arc had matured and a variety of syn- to late-orogenic igneous rocks appeared in both tensional and compressional settings. Shortly thereafter, the Svecofennian magmatic activity ceased altogether, probably as a result of collision between the arc and the Archaean continent in the north. It is also suggested that pre-Svecofennian rifting of the Archaean craton had created a passive continental margin and that the transition to an active margin with subsequent island-arc magmatism and subduction beneath the Archaean craton commenced prior to 1930 Ma ago. It may well have been initiated by a relative drift of the Archaean craton towards the present southwest as a consequence of the formation of the collisional Proterozoic Lapland Granulite Belt in the northernmost Baltic Shield.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

Applied Geology

Tillämpad geologi

Ore Geology

Malmgeologi

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