Paleomagnetic and Thermomagnetic Studies on Rock Samples from COSC - 1 Drilling Project

Sammanfattning: The COSC-1 borehole located in the Lower Seve nappe of the Central Scandinavian Caledonides is intended to study the tectonic evolution of the Paleozoic orogen. The drilling project reached a depth of 2495.8m and obtained samples from different lithologal units of mica schist, amphibolite, gneiss, and mylonitic gneisses.     To test if the samples are suitable for paleomagnetism, laboratory measurements of natural remanent magnetism are performed on sub-samples of the COSC-1 drill core in the paleomagnetic laboratory with alternating field demagnetization, IRM acquisition as well as the temperature dependence of susceptibility measurements. Important properties of the samples such as coercivity, Curie temperature, inclination, and declination are determined with the measurements.     Most of the samples carry a remanent magnetization that can be readily demagnetized with alternating field demagnetization up to 100 mT. Some of the samples may be suitable for paleomagnetism, with the major ferromagnetic mineral compositions of magnetite, hematite, and FeTi oxides. However, low coercivities and median destructive fields suggest that the magnetite-bearing samples will be prone to remagnetization, making them more challenging to use in terms of retrieving a primary magnetization originating from the Caledonian orogeny. The thermomagnetic results of some samples reflect the metamorphic conditions experienced by the rocks and the mineral assemblage changed irreversibly during step-wise heating experiments. These results can possibly be used as an indicator for the metamorphic temperature experienced by the different lithologal units. Although further measurements are needed to get a clearer understanding of the suitability of the COSC-1 sample for paleomagnetic reconstructions (including thermal demagnetization experiments), this thesis indicates that the COSC-1 rocks contain interesting paleo- and rock magnetic features that are worth further study.