CRYSTALLIZATION FROM STRATIFIED MAGMAS IN THE HONNINGSVAG INTRUSIVE SUITE, NORTHERN NORWAY - A REAPPRAISAL

Wedge-shaped layers of ultramafic and mafic cumulates in Intrusion II of the Caledonian Honningsvag Intrusive Suite suggest crystallization on an inclined magma chamber floor from a compositionally-zoned and de nsity-stratified magma. Cyclic unit 8 (140-100 m thick) consists of a distally-thinning olivine gabbro (denoted paoC) macrolayer overlain by a distally-thickening gabbronorite, pahC. New mineral data in four tr averses across cyclic unit 8 show systematic compositional changes; th e Mg# of the mafic phases decreases upwards through the unit and dista lly, both along the base and along the paoC/pahC interface. A crystall ization model based on an effectively continuously-zoned magma chamber with numerous, relatively thin, double-diffusive magma layers is prop osed. Differential migration of horizontal isopleths (e.g. Mg# and a(s io2)) in response to fractional crystallization and assimilation of co untry rock can explain the variations in the Mg# of the cumulates.