Alkaline magmatism, water-rock interaction and multiple metamorphism in the Seiland Igneous Province, Northern Norway

• Main Author: Li, Xiaoyan
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2013
• Subjects: Nordnorwegen; Metamorphose (Geologie); Magmatismus; Zeolith; Online-Ressource; Norway; Seiland; Øksfjord; Northern Norway
• Online Access: https://freidok.uni-freiburg.de/data/9262; https://nbn-resolving.org/urn:nbn:de:bsz:25-opus-92622; https://freidok.uni-freiburg.de/dnb/download/9262

In this PhD thesis, I present investigations on the autometamorphism in the nepheline syenite from Stjernøy island (Part I), and the zeolite formation (Part II) and rare stronalsite-banalsite solid solution (Part III) during hydrothermal events of nepheline syenite. In addition, water samples from the nepheline syenite-carbonatite catchment were analyzed and further explained through the zeolite formation (Part IV). Metamorphism in Øksfjord Peninsula was demonstrated by multiple metamorphism in contact aureole of the Reinfjord ultramafic complex (Part V), and metamorphism of paragneisses from other five locations (Part VI). In Part I, textures of nepheline syenite indicate a complex succession of reactions during cooling from an igneous crystallization stage to late hydrothermal events. Based on microscopic observation of primary and secondary minerals in the rock samples, the derived reactions, and the thermodynamic modeling for mineral assemblages, several conclusions concerning the evolution of nepheline syenite can be drawn: (1) Orthomagmatic stage of nepheline syenite is characteristic with assemblage of nepheline + K-feldspar + clinopyroxene + amphibole ± magnetite ± ilmenite at temperatures between ca. 500-700 ˚C at activity of silica being ca. 0.15-0.33. (2) Autometamorphic stage is represented by coronas of amphibole on clinopyroxene and biotite on amphibole, which are result from reactions between primary minerals and residual melt. (3) Hydrothermal stage I is impressed by pervasive natrolite transformed from nepheline and albite dissolution. The related fluid is considered as fluid expelled by crystallizing magma, which has decreasing silica activity and slightly increasing Na activity with the product of natrolite. (4) Hydrothermal stage II is dominated by infiltration of Ca-HCO3 fluid from carbonatite catchment into the nepheline syenite along fractures which resulted in the generation of thomsonite by transformation from nepheline and natrolite. In Part II, I describe two hydrothermal stages in ...