The Vaasa Migmatitic Complex (Svecofennian Orogen, Finland)

Buildup of a LP‐HT Dome During Nuna Assembly

Document identifier: oai:DiVA.org:ltu-77985
Access full text here:10.1029/2019TC005583
Keyword: Natural Sciences, Earth and Related Environmental Sciences, Geology, Naturvetenskap, Geovetenskap och miljövetenskap, Geologi, Migmatitic compelx, HT-LP metamorphism, Paleoproterozoic accretionary orogen, Channel flow, Oroclinal buckling
Publication year: 2020
Abstract:

Tectonic evolution of the Paleoproterozoic Vaasa migmatitic complex (VMC) in the central part of the Svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps, deep seismic and magnetotelluric profiles, and structural and metamorphic data. The VMC is a semicircular structure with migmatitic rim and granitic core composed of several subdomes. It evolved in three main tectonic events (D1–D3). The D1 event (ca. 1.89–1.88 Ga) corresponds to the stacking of supracrustal rocks and the formation of an inverted metamorphic gradient. Anatexis at LP‐HT metamorphic conditions enabled the material to flow. The D2 event (ca. 1.88–1.87 Ga) corresponds to large‐scale folding of the partially molten crust within an orocline. It is marked by folds with an E‐W vertical axial planar foliation. The late D3 event resulted from mass redistribution owing to mechanical instabilities within the hinge of the orocline. It is marked by vertical shearing (ca. 1.87–1.85 Ga) in the marginal parts of the complex and along the granitoid subdomes. The seismic reflection profile (FIRE 3a) and magnetotelluric profiles (MT‐PE and MT‐B2) image large‐scale D1 stacking structures within an accretionary prism. Near vertical breaks in crustal‐scale reflectivity and conductivity models are interpreted as D3 shear zones. The VMC is an example of early mass and heat transfer within a collage of hot supracrustal rocks in an accretionary belt. Partial melting enhanced the flow of material, the production, and rise of magma as well as exhumation, marked by magmatic domes in the hinge of the orocline.

Authors

Francis Chopin

Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland. Université de Strasbourg, CNRS, IPGS UMR 7516, Strasbourg, France. Center for Lithospheric Research, Czech Geological Survey, Prague, Czech Republic
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Annakaisa Korja

Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
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Kaisa Nikkilä

Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland. Geology and Mineralogy, Åbo Akademi University, Turku, Finland
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Pentti Hölttä

Geological Survey of Finland, Espoo, Finland
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Toivo Korja

Faculty of Technology, Oulu Mining School, Applied Geophysics, University of Oulu, Oulu, Finland
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Mohamed Abdel Zaher

Faculty of Technology, Oulu Mining School, Applied Geophysics, University of Oulu, Oulu, Finland
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Matti Kurhila

Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland. Geological Survey of Finland, Espoo, Finland
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Olav Eklund

Geology and Mineralogy, Åbo Akademi University, Turku, Finland
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O. Tapani Rämö

Department of Geosciences and Geography, University of Helsinki, Helsinki, Finland
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