A detailed field and geochemical investigation of the volcanic sequence in the Grimelid-area: The Solund-Stavfjord Ophiolite Complex
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This master thesis focuses on the volcanic sequence of the Solund-Stavfjord Ophiolite Complex (SSOC) in Grimelia, in order to provide more detailed information and a better understanding of the development. The SSOC (443 Ma, ± 3 Ma) is located within the western parts of the Norwegian Caledonides, between Solund and Bremanger, and represents a remnant of the Iapetus oceanic lithosphere evolved in the Caledonian marginal basin. As a result of detailed fieldwork and thorough mapping of the sequence, a Master profile of Grimelia is constructed with a division into two parts. The first 500 m of the sequence is represented by the first part, which is furthermore divided in two parts (Part 1A and 1B), due to major differences within short distances. Part 1B is located near by the Grimelia mines and is therefore composed of varying degree of VMS deposits. It is, however, important to highlight that this will not be the focus of the thesis but considered with general knowledge about mineralization at spreading ridges. A proposed model for the Grimelia deposits is hence presented, which will suggest the controlling factor for the formation of VMS deposits in Grimelia. The volcanic sequence, represented by the Master profile, is composed of three main components, 1) massive sheet flows, 2) pillow lavas, and 3) volcanic breccias. By measuring the vertical and horizontal axis of the different pillows, as well as other factors further discussed, it will be possible to calculate and predict the degree of deformation in the area, and hence, reconstruct the volcanic sequence to an estimated new thickness. Before reconstruction, the Master profile is measured to be 1205 m, excluding the metasedimentary cover of metagraywacke and phyllite. However, various calculations propose an estimated original thickness of 1430 m, which makes this, yet the longest registered volcanic sequence of the SSOC. Last, but not least, several samples of metabasalts are collected from the study area, leading to a geochemical investigation for parts of the SSOC. Previously studies from the SSOC suggests that the metabasalts are formed from magmas that were produced in a trench-distal suprasubduction-zone setting, sufficiently far from the subducting slab with only minor influence of slab-derived fluids. The various presented diagrams of this study compliment the numerous studies of the SSOC, reflecting minor subduction influence for some of the presented components, yet a dominance of a subduction-unrelated character.
Postponed access: the file will be accessible after 2023-12-08