Analog models of the lateral spreading of a thick three-layer crust : implications for the Svecofennian orogen in Finland

• Main Author: Nikkilä, Kaisa
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: Åbo Akademi University 2016
• Subjects: Fennoscandian
• Online Access: https://research.abo.fi/en/publications/bd36a1ac-7f4d-464e-9e6d-26a4bb617fa2; http://urn.fi/URN:ISBN:978-952-12-3430-9; https://urn.fi/URN:NBN:fi-fe202201147050

Our knowledge of the crustal structure of the Precambrian Svecofennian orogen has been enhanced during the last decade. Much of the new knowledge is due to the deep seismic reflection studies (Finnish Reflection Experiments; FIRE), which transect the main lithological units and tectonic boundaries on the Finnish side of the Fennoscandian Shield, showing a frozen image of the crustal structure. Understanding of the crustal structures improves interpretations of crustal evolution. However, the tectonic events and processes causing the anomalies/structures cannot be directly defined from the profiles. The processes can be studied by analog modeling, which is a viable tool for filling in absent components of a puzzle of reconstruction of the crustal evolution. The analog modeling can yield information on the generation and the development of crustal scale structures and crustal components, for example, after mountain building process. In this thesis, post-accretion crustal evolution of thickened orogenic crust is studied via analog modeling. Geochronological, geochemical and geophysical data from the central part of the Svecofennian orogen are used to compare analog models to nature.The thesis presents two sets of analog modeling experiments, thermomechanical and centrifuge, which are simulating the lateral spreading of a three-layer crust after thermal relaxation. In the modeling experiments, it is assumed that the spreading is caused by the differences in gravitational potential energy between the thickened orogenic crust and the adjacent thinner areas. In the experiments, the spreading is dictated towards free space. In the centrifuge modeling, the spreading is gravitationally induced and produces lateral flow and ductile uplift. In the thermomechanical modeling, the spreading is thermally induced and it only produces lateral flow.The analog modeling results show that a thick accretional orogenic crust with ductile middle layer will undergo lateral and gravitational spreading in all crustal layers. The spreading ...