Petrological analyses and Lu-Hf geochronology of subducted continental and oceanic crust from different locations in the upper and lower plate of the Caledonian Orogen

• Main Author: Faßmer, Kathrin
• Other Authors: Froitzheim, Nikolaus, Nagel, Thorsten J.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universitäts- und Landesbibliothek Bonn 2020
• Subjects: ddc:500; Greenland
• Online Access: https://hdl.handle.net/20.500.11811/8293

In this thesis I conducted Lu-Hf analyses on samples from locations all over the Caledonian Orogen. I combined these ages with petrological analyses in order to help to unravel some of the open questions concerning the development of the Caledonian continental collision. I dated three meta-mafic / meta-ultramafic samples from the Northeast Greenland Eclogite Province but only one of the eclogites gave a precise isochron age of 357.8 ± 1.7 Ma. I interpret this age as dating a point shortly after the pressure-peak. This sample shows textural evidence of UHP metamorphism, which is in accordance with a c. 360 Ma age from another UHP rock from further northeast. The other eclogite and the ultramafic sample experienced probably only HP metamorphism and yielded errorchrons which are caused by a scatter of the garnet separates due to protracted garnet growth and partial re-equilibration of garnets during high temperature at peak-pressure conditions. Nevertheless, a geological meaningful age of c. 400 Ma age can be estimated for high-pressure metamorphism of those samples which is in accordance with previous dating for HP rocks from the Northeast Greenland Eclogite province. These results support the idea that UHP metamorphism in the Northeast Greenland Eclogite Province is c. 360 Ma, while HP metamorphism is c. 400 Ma. In addition this study showed that UHP metamorphism is not restricted to the Eastern Block of the Northeast Greenland Eclogite Province, but also occurs in the Central Block. The two main problems when explaining these ages is that the Northeast Greenland Eclogite Province is interpreted to be the Laurentian continental margin (i.e. upper plate) and that UHP metamorphism occurred after the main collisional phase between Baltica and Laurentia. Based on my analyses I support a tectonic model in which HP metamorphism at 400 Ma was caused by crustal thickening during collision between Baltica and Laurentia and UHP metamorphism at c. 360 Ma was caused by intra-continental subduction within Laurentia. I ...