The Vaasa Migmatitic Complex (Svecofennian Orogen, Finland): Buildup of a LP‐HT Dome During Nuna Assembly

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.

HTLP metamorphism and fluid‐fluxed melting during multistage anatexis of continental crust (N Sardinia, Italy)

“…Regardless of the effectiveness of melt redistribution during M2, the P–T–t‐d path captured by diatexite implies HTLP metamorphism and anatexis in the uppermost part of the continental crust, a condition which is rarely documented in convergent settings (i.e. Chopin et al, 2020).…”

“…Burg & Gerya, 2005; Nabelek et al, 2010; Platt, 2015). A further complication for deciphering the heat budget is that all these mechanisms are potentially complementary, at least on a local scale; therefore, the geodynamic significance of HTLP metamorphism remains contentious (Chopin et al, 2020; Pownall, 2015; Savko et al, 2015).…”

Contribution of bedrock structures to the bedrock surface topography and groundwater flow systems within deep glaciofluvial aquifers in Kurikka, Western Finland

“…OSB is lithologically dominated by biotite paragneisses and structurally characterised by the ENE‐WSW striking, dextral Vittinki high‐strain zone (Pääkkönen, 1966) occurring approximately 30 km north of the study area and NE‐SW striking ductile shear zones abutting the Vittinki zone at the central parts from the Southwest (Figure 1b; Vaarma & Kähkönen, 1994; Lehtonen et al, 2005). Structural signatures within the study area and its surroundings have been attributed to the coupled Bothnian oroclines (Lahtinen et al (2017) bounded by the migmatitic Vaasa Complex (VC; Chopin et al, 2020) in the west and the CFGC in the east (Figure 1a).…”

A Combined Model of the Diapiric and Collisional Formation Mechanism of the Paleoproterozoic Granite-Migmatite-Gneiss Domes of the Svecofennian Belt

“…Эволюция термальной структуры -купола Вааса [Chopin et al, 2013] -отображает температурную эволюцию и реологическое поведение корового вещества во время орогенеза. В ядре этого купола развиты гранитоиды, которые с восточной стороны обрамляются Ботническим метаморфическим поясом.…”