The post-Caledonian history of the Røldal Shear Zone (SW Norway): an apatite fission track study

The post-Caledonian tectonic history and landscape evolution of southwestern Norway is not very well understood and therefore the subject of an ongoing debate. The lack of onshore post-Devonian sediments makes the study of vertical movements in the upper few kilometers of the crust a challenge. At the present time, the only means for constraining upper crustal movements directly are thermochronological analyses. Apatite ssion track analysis was applied with an aim to shed light on the post-Caledonian history of the Røldal Shear Zone area. The Røldal Shear Zone is a major shear zone running parallel to the Hardangerfjord Shear Zone located north of the study area. The Røldal Shear Zone is, however, much less studied. The apatite ssion track analyses yielded Permian to early Cretaceous ages with the majority of Jurassic ages. The ages are generally decreasing from the coast towards the inland, and are clearly o set across the Røldal Shear Zone. Inverse thermal history modeling was applied to four samples from the coast, representing the hangingwall and footwall, and the inland, respectively. The modeling suggested rapid Permo-Triassic cooling for the coastal samples, but slower and more constant cooling until the Cenozoic for the inland sample when it accelerated. This is suggested to re ect a rift related rift ank uplift in the coastal area, whereas the inland sample was much less a ected by this uplift. The modeling for the coastal samples also suggested the samples to have been at (or close to) the surface in the Jurassic and was subsequently re-buried in the Cretaceous. This is not the case for the inland sample which reached the surface in the Cenozoic. The cooling rate accelerated dramatically in the Neogene. This is suggested to be a result of increased erosion rates due to the shift to a colder global climate. It is suggested that the evolution of the landscape of southwestern Norway is a result of sustained elevated topography shaped by rift-related uplift, extensional faulting and erosion since the Caledonian Orogeny. Acknowledgement There are a number of people who have helped and supported me during my time as a master student at the University of Bergen. I am most grateful to each and every one of you! First of all I would like to extend my sincere gratitude to my supervisors, Dr. Anna Katharina Ksienzyk and Prof. Joachim Jacobs, for excellent guidance and support during my master project. Anna, I thank you for teaching me the method, commenting on my work, great advice and helping me whenever I was in need of it. Joachim, I thank you for great advice, fruitful discussions and help with organization. I am very grateful to Tobias Woznitza who provided me with additional samples, and for proof-reading parts of my work. I would also like to thank Tereza Konopaskova and Irina Maria Dumitru for teaching and helping me with the mineral separation and grain mount preparation. You made the long hours of lab work y by! I also thank Yuval Ronen for etching my mica detectors. I would like to extend a special thanks to my good friends Christian Rønnevik, Thomas Berg Kristensen, Hallgeir Sirevaag, Julia Linn Nævdal, Karen Johannessen, Mona Karin Boge and Emilie Randeberg for your constant encouragement, cheerfulness, help and friendship. You guys are the best! Christian is especially thanked for helping me with the software whenever I had problems and for proof-reading some of my work. Without you, I would still be working on the front page! Karen has also read and commented on some of my work which I am very grateful for. I would also like to thank all my other friends for being the nicest and most amazing friends I could ever ask for. I thank the people in the thermochronology group at the University of Bergen for a great time with fun stories and good cakes on our weekly meetings. I would also like to thank my parents, Borghild and Brynjulf Hermansen, for always supporting me, for showing interest in what I do, and for helping me in so many di erent ways during my time at the university. I thank my crazy, supernice siblings and their families for always making me laugh and for keeping me sane when I was caught between a rock and a hard place. I thank my boyfriend, Rune Uldum Flyvholm, for assisting me during eld work in the blizzard in January of 2014 (! ) and the following mineral separation. I also thank you for encouraging me to always do my best, and for always being there for me.