Kaisa Nikkilä

Åbo Akademi University · Department of Geology and Mineralogy

The magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse. Chemical composition, age and structure give information about the magma source and emplacement depths. The target of this study is the Central Finland batholith (CFGC) that provides...

Southern Finland consist of belts of migmatitic infra-and supracrustal rocks. The southernmost migmatitic belt and Uusimaa belt have coeval and presumably similar tectonic histories, although it is proposed that they are separated by a terrane boundary. In this study, we investigated leucosomes, granitic intrusions and deformation history in the so...

Leucosome sizes in migmatites has been shown to follow power-law distribution, which is indicative of self-organized criticality governing accumulation and transport of partial melts in anatexis. In our measurements of leucosome widths in the Olkiluoto migmatite in western Finland, we found double power-law distributions in addition to single power...

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...

The Paleoproterozoic Svecofennian orogenic domain of Southern Finland consists principally of belts of strongly migmatized infra- and supracrustal rocks in upper amphibolite to granulite facies, with areas of less migmatized rocks in between. The granite-migmatite belts are presumably related to each other. However, the relationship between the for...

The Vaasa migmatitic complex (VMC), which is a part of the Paleoproterozoic Svecofennian accretionary orogen, has been studied by geological and geophysical methods. Lithological, structural, geochronological (U/Pb) and geophysical (MT and seismic reflection sections, aeromagnetic and gravity maps) data are used to interpret the structure and forma...

The Paleoproterozoic Svecofennian orogenic domain of Southern Finland consists principally of belts of strongly migmatized infra- and supracrustal rocks and granitoids in upper amphibolite to granulite facies, with areas of less migmatized rocks in between. The granite-migmatite belts are presumably related to each other. However, their structural...

Many inherited structures and mechanical components affect to the post-collisional evolution in orogens. Here I present the effect of the crustal scale shear zones in a weak vs. a rigid crustal blocks during a post-collisional lateral spreading. The results are based on two analog modelings and discussion in a dissertation (Nikkilä et al., 2009; 20...

The central part of the Paleoproterozoic Svecofennian orogen formed in arc-collision at 1.91 Ga. The collision led to crustal thickening and partial melting of the crust. The partial melting formed a large batholith (Central Finland granitoid complex; CFGC) at the upper-middle crustal transition zone and a weak middle crust, which enabled crustal s...

Arc-collisional batholiths may record their magmatic history from an arc to arc-collision zone, hence the batholiths mirrors the underlying crustal evolution. Change in the geochemical composition, age and structure can give direct and indirect information of the changing tectonic setting. We have used the Central Finland granitoid complex (CFGC) i...

Geodynamic models offer insight into deformation styles of syn- and post-collisional extensional processes. Such models often ignore the effect of lateral viscosity contrast between accreted terranes and inherited tectonic boundaries. This paper presents a set of crustal-scale analog experiments of one-way post-collisional gravitational spreading t...

Over-thickened orogenic crust may suffer from rheological, gravitational and topographical unbalancing resulting in discharging via gravitational spreading. If the thickened orogen is also hot, then increased temperature may reduce the viscosity of the crust that may induce large-scale horizontal flow. The effect of flow on the crustal architecture...

The Paleoproterozoic Svecofennian orogenic domain encloses the Central Finland granitoid complex (CFGC). The complex consists of plutonic rocks and minor amounts of supracrustal and subvolcanic rocks. The magmatism is associated with syn- and post-convergent orogenic events at 1890-1870 Ma. However, the age data is defective with major uncertaintie...

Orogenesis can develop at different scales and between different plate types and may result in overthickening of the crust and thus post-collisional extension (Beaumont et al. 2001). This paper presents crustal scale structures of unilateral gravitational spreading in three-layered crust at post-collisional stage using analogue centrifuge models....

In the Paleoproterozoic Svecofennian orogenic domain of the Fennoscandian shield, the large Central Finland Granitoid Complex (CFGC) consists of plutonic rocks and minor amounts of supracrustal rocks. The CFGC has a geological history that is only vaguely known. The metamorphic culmination of the Svecofennian orogen occurred at about 1890 Ma. The r...

After collision, partial melting takes place in thermally relaxed parts that are at depths greater than 25 km. Low density and viscosity magmas rise up to depths of 12 to 15 km where it is emplaced as flat-lying granites. Shearing helps to segregate magma and to guide it toward the surface. The Paleoproterozoic Svecofennian orogenic domain of the F...

The exposed Svecofennian crust (50-65 km) has been suggested to have thickened in continental accretion between Archean and Paleoproterozoic terranes, probably at a high convergence rate. It is likely that this thickened orogen experienced lateral spreading during its final stages. This post-orogenic event has reshaped the collisional framework and...

After collision, partial melting takes place in thermally relaxed parts that are at depths greater than 25 km. Low density and viscosity magmas rise up to depths of 12 to 15 km where it is emplaced as flat-lying granites. Shearing helps to segregate magma and to guide it toward the surface. The Paleoproterozoic Svecofennian orogenic domain of the F...

Supercontinental cycle build continents and breaks them. Continental collision zones withhigh topographic relief can develop during supercontinental cycle. In collision zones, plates can rotatethe direction of movement locally. When an orogenic belt with high mountain range and thicklithosphere has reached a substantial thickness, the orogen grows...

The modeling exercise simulated the late Svecofennian orogen processes in the Central Finland area. The Svecofennian orogeny in the Northern Europe is characterized by low pressure and high temperature metamorphism (1.88 Ga). The environment was similar to that presently in Tibetian plateau. We assume the thickened continental crust were 80 kilomet...

Svecofennian Orogen is a Paleoproterozoic analogue of a laterally spreading accretionary orogen at a convergent margin setting. The exposed parts that are composed of granitoid intrusions as well as metamorphosed and highly deformed supracrustal units representing paleo-lower-upper and paleo-upper-middle crust. Both the exposed bedrock surface and...

The modeling exercise simulated the late Svecofennian orogen processes in the Central Finland area. The Svecofennian orogeny in the Northern Europe is characterized by low pressure and high temperature metamorphism (1.88 Ga), and the continental crust was very thick after the collision. The environment was similar to that presently in Tibetian plat...

We present a set of analogue experiments simulating the extensional collapse of the Svecofennian orogeny. The experiments were conducted in a new thermomechanical deformation apparatus at Frankfurt University using plasticine as an analogue material. Layered models (upper crust, middle crust and lower crust) were constructed and subjected to extens...