Deformation, Phyllonitization and Associated Element Mobilization of Granitoid Rocks.
Deformation, Phyllonitization and Associated Element Mobilization of Granitoid Rocks.
Previously Published Material: Presented as a poster with preliminary results at the Winter Conference 2015 in Stavanger, Norway. Hosted by the Geological Society of Norway.
Abstract ID#: 35616
English Abstract:
This study investigates the mobilization of the major and trace elements related to deformation and associated phyllonitization of the Fagervika granitoid. East of Trondheim, Norway lays the area of Bymarka, that is a part of an ophiolite complex that is dominated by greenstones and several felsic intrusives, including the Fagervika granitoid that is the largest. The granitoid extends approximately 7 km inland, from the shore of Trondheimsfjorden and southwards towards Skjelbreia Lake where it fingers out. Extensive detail mapping of the Fagervika granitoid in the area around Gråkallen reveals an area with varying degrees of deformation and associated phyllonitization, including occurrences of sulphide-bearing hydrothermal quartz in association with the deformation zones. Two types of deformation zones were recognized. 1. Millimetre to centimetre mica- and epidote-rich zones with dynamically recrystallized quartz. 2. Decimetre to meter wide zones with quartz, muscovite, little or no feldspar, except a few albite porphyroblasts and varying degrees of deformation, from protomylonite to mylonite. The least deformed samples have a magmatic texture, but the feldspars shows weak sericitization and saussuritization. With increasing degree of deformation, the feldspars disappear and muscovite appears, revealed by the loss of Na, Ca and Eu and gain of K. There is also a relationship between the relative amount of recrystallized quartz to clast ratio and the amount of trace element mobilization. Comparisons of the least and most deformed samples are shown by examining mineral assemblages and textures, along with quantitative geochemical and mineralogical data. Isocon diagrams and quantitative Rietveld will be used to infer which major and trace elements and minerals that have been mobilized during deformation. The next step will be to compare the geochemical data to microscopic investigations, and SEM, microprobe and laser data will be used to accurately determine the mineral chemistry of the different mineral phases. By using principles of geochemistry, the goal is to understand the element mobility path of the different elements and minerals in the granitoid during deformation.