Geodynamics and Basin Studies


Physical and chemical processes in a large magma chamber: The Bjerkreim-Sokndal Intrusion

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Project coordinator: Professor Brian Robins
Project partners: Docent J. Richard Wilson

Funding: The Norwegian Research Council

Principal investigator: Professor Brian Robins

People involved at UiB: Professor Sven Maaløe Ph.D. student Federico Chiodoni

Project period: 2005-01-01 to 2007-04-30

Physical and chemical processes that take place in magma chambers are of fundamental importance for magma differentiation, mixing and contamination as well as the nature and products of volcanic activity. However, despite considerable research effort over many years there is currently little consensus among petrologists regarding the detailed nature and relative importance of the processes that take place in magma chambers, and much remains to be revealed about their evolution. One approach to the evaluation of processes in magma chambers is the study of layered intrusions, i.e. solidified magma chambers now exposed at the surface of the Earth. These intrusions contain layered series, i.e. rocks that crystallised successively on the roof, walls and, most commonly, on the floor of the respective magma chamber. Layered series are records of temporal and/or spatial variations in the composition and temperature of the magma occupying the chamber. The study of layered series in solidified magma chambers can therefore contribute to an identification and evaluation of the processes and events that have taken place during their evolution. The project aims to complete a detailed documentation of the >7km thick Layered Series of the Proterozoic Bjerkreim-Sokndal Intrusion, the largest and compositionally most unusual of the Norwegian layered intrusions, and hence the physical and chemical processes that occurred in a specific large magma chamber. During the course of the project the following specific topics will be addressed through mapping and sample collection in the field, mineral analysis and whole-rock major, trace-element and isotope geochemistry using relevant techniques currently available in laboratories at the Department of Earth Sciences, University of Bergen (EMP, XRF, TIMS, ICP-MS and LA-ICP-MS): * The field relations, mineralogy and petrology of the Layered Series in the southern, Sokndal lobe of the intrusion, its correlation with the much thicker layered series developed in the Bjerkreim lobe and its relation to replenishment and lateral magma-chamber enlargement; * The structure, mineralogy, geochemistry of the uppermost units in the intrusion (mangerite, quartz mangerite and charnockite), their relationship to the underlying Layered Series and their possible genesis by liquid immiscibility; * The geochemistry of ilmenite-rich layers and sequences in regressive intervals in the Bjerkreim Layered Series and their relation to magma mixing during episodes of chamber replenishment.