The nature and origin of an anorthosite associated ilmenite-rich leuconorite, Hakefjorden Complex, south-west Sweden

Ilmenite-rich leuconorite (IRL) occurs in the Neoproterozoic Hakefjorden Complex (HFC; a norite–anorthosite intrusion) in south-western Sweden. The medium to fine-grained IRL comprises a disc-shaped, subhorizontal unit within the complex with gradual transitions into the host norite. It is character...

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Bibliographic Details
Published in:Lithos 2000-03, Vol.51 (3), p.247-267
Main Authors: Årebäck, Hans, Stigh, Jimmy
Format: Article
Language:English
Subjects:
Anorthosite
Fe–Ti oxides
Ilmenite-rich leuconorite
Norite
Sveconorwegian
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Description
Summary:Ilmenite-rich leuconorite (IRL) occurs in the Neoproterozoic Hakefjorden Complex (HFC; a norite–anorthosite intrusion) in south-western Sweden. The medium to fine-grained IRL comprises a disc-shaped, subhorizontal unit within the complex with gradual transitions into the host norite. It is characterised by a well-developed subhorizontal magmatic foliation, displayed by the preferred orientation of tabular plagioclase crystals, and it consists of subequal amounts of labradorite and ilmenite with minor interstitial orthopyroxene. The IRL contains a variety of inclusions comprising decimeter- to meter-size anorthosite and norite blocks from the hosting HFC, and millimeter- to decimeter-size magmatic segregations, formed within the IRL-unit, such as Fe–Ti oxide-, fine-grained anorthosite- and fine-scale igneous layered plagioclase–orthopyroxene inclusions. The latter are disc- to sheet-shaped, usually concordant to the foliation and interpreted to represent igneous layers disrupted during deformation in the magmatic state. The deformation also caused the magmatic foliation during simple shear conditions (no lineation is observed), which wraps around all inclusion types. Fractional crystallization starting with deep crustal anorthosite and ultramafic differentiation produced a late stage liquid unusually enriched in Fe and Ti. Such a liquid with plagioclase in suspension is put forward as parental for the IRL. Fe–Ti oxide subsolidus re-equilibration during slow cooling modified the oxide compositions and textural relations indicate that annealing and textural coarsening played an important role in the formation of the densely packed Fe–Ti oxide inclusions.
ISSN:0024-4937
1872-6143
DOI:10.1016/S0024-4937(99)00070-5