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Olivine-rich units in the Fongen–Hyllingen Intrusion, Norway: implications for magma chamber processes |
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| Authors: | Gurli B Meyer and J Richard Wilson |
| Institution: | a Geological Survey of Norway, Leiv Eirikssons vei 39, N-7040 Trondheim, Norway b Department of Earth Sciences, University of Aarhus, 8000 Århus C, Denmark |
| Abstract: | The Fongen–Hyllingen Intrusion (FHI) is considered to have crystallised from stratified magma residing in a bowl-shaped magma chamber. Seven olivine-rich units, representing the most primitive cumulates in the central part of the intrusion, are associated with compositional reversals and are interpreted as having formed at the lowest part of the magma chamber floor. Based on phase-relationships, the crystallisation order is explained in terms of magma mixing and fractional crystallisation. Repeated influxes of small volumes of dense, primitive magma at the base of the chamber had a major impact on the crystallising assemblage on the local floor and a decreasing effect towards the flanks of the chamber. This was due to the small volume of replenishing magma, the geometry of the chamber and the consequent restriction of magma mixing to the deepest part of the chamber where the new magma was emplaced. It is estimated that the chamber floor sloped as little as 1–2°, but this was sufficient to give widely different cumulate sequences near the bottom of the chamber and on the flanks. |
| Keywords: | Fongen–Hyllingen Intrusion Layered intrusion Cumulates Mineral composition Magmatic differentiation Poikilitic texture |
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