Browsing by Author "Teräs, Oliver"

This MSc thesis is built on drill core and outcrops data at the Haukivuori area where fluorite bearing granitoids cut sharply the country rocks (mafic volcanic rocks). This thesis presents new whole-rock geochemical and zircon uranium-lead age data for Haukivuori granitoids in southeast Finland, which provide insights into the distribution of post-collisional granitoids in this region. The purpose of this thesis is to classify a granitoids in Haukivuori and to determine the conditions of their formation. Tectonic evolution of the central and southern Finland is also reviewed and the relationships between Haukivuori whole-rock geochemical data and already published whole-rock data from southern Fin-land post-collisional granitoids are discussed. In the present thesis, the focus is on the 1.815–1.77 billion years post-collisional granitic magmatism across the southern Finland. Haukivuori granitoids modal compositions vary from quartz-monzonite through granite to granodiorite. The contents of quartz, K-feldspar and plagioclase remain consistent all in all, covering about 95 % of the mineral assemblage. The accessories are biotite, muscovite, fluorite, calcite, apatite and zircon as well as oxides. Granitoids show high-K calc-alkaline to shoshonitic affinities and are metaluminous to weakly peraluminous with enrichment in light rare earth elements (example lanthanum normalized to chondrites shows ratios between 93 to 4263) and granitoids lack significant europium anomalies. Granitoids show enrichment in large-ion lithophile elements such as barium (1359–10000 ppm) and strontium (827–8318 ppm), and they display negative anomalies on chondrite normalized spider diagrams in high field strength elements such as niobium, tantalum, zirconium, and titanium. Concordia-intercept age from zircons uranium-lead data of 1794 ± 13 million years is the best crystallization age estimate for the Haukivuori granitoids. Haukivuori granitoid’s age, their undeformed nature, and the fact that granitoids cut country rocks clearly put granitoids into the post-collisional group. Thus, Haukivuori granitoids can be classified as post-collisional granitoids. Haukivuori granitoids display all features of typical high Barium-Strontium granitoids. Thus, granitoids are interpreted to represent a high-level expression of the mantle magmatism that was derived from depleted mantle source which was enriched during an earlier subduction episode.