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 Co mplex (HFC; a norite-anorthosite intrusion) in south-western Sweden. The me dium to fine-grained IRL comprises a disc-shaped, subhorizontal unit within the complex with gradual transitions into the host norite. It is character ised 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 orthop yroxene. The IRL contains a variety of inclusions comprising decimeter- to meter-size anorthosite and norite blocks from the hosting HFC, and millimet er- to decimeter-size magmatic segregations, formed within the IRL-unit, su ch as Fe-Ti oxide-, fine-grained anorthosite- and fine-scale igneous layere d plagioclase-orthopyroxene inclusions. The latter are disc- to sheet-shape d, 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 line ation is observed), which wraps around all inclusion types. Fractional crys tallization starting with deep crustal anorthosite and ultramafic different iation 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 I RL. Fe-Ti oxide subsolidus re-equilibration during slow cooling modified th e oxide compositions and textural relations indicate that annealing and tex tural coarsening played an important role in the formation of the densely p acked Fe-Ti oxide inclusions. (C) 2000 Elsevier Science B.V. All rights res erved.