Journal of Petrology, Volume 39, Issue 4: April 1 1998.

The Skaergaard Layered Series. Part IV. Reaction-Transport Simulations of Foundered Blocks

ERIC L. SONNENTHAL¹ AND ALEXANDER R. McBIRNEY²

¹EARTH SCIENCES DIVISION, LAWRENCE BERKELEY NATIONAL LABORATORY, UNIVERSITY OF CALIFORNIA,MS90-1116, BERKELEY, CA 94720, USA ²DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF OREGON, EUGENE, OR 97403, USA

During the middle stages of crystallization of the Skaergaard Layered Series large numbers of blocks became detached from the Upper Border Series and settled into the mush of crystals on the floor. It has been recognized for some time that these blocks now have compositions and textures that differ markedly from those of the units from which they came. They tend to be more plagioclase rich and seem to have lost mafic components to the surrounding gabbro. Numerical simulations coupling crystallization, melting, and heat and mass transfer for a multicomponent system show how the blocks reacted with the mush in which they were emplaced. Enhanced cooling and crystallization of a compositionally stratified mush adjacent to the blocks resulted in patterns of melt compositions similar to those of layering around the blocks. Volume changes during crystallization and melting induced convection of the interstitial melt leading to changes in the bulk compositions of the blocks and the surrounding mush. Inhomogeneities such as inclusions are likely to facilitate the onset of compositional convection in a chemically stratified solidification zone.

Keywords: assimilation;convection; reaction-transport modeling; Skaergaard Intrusion; solidification zones

Pages 633-661

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