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The Unit 12 allivalite, Eastern Layered Intrusion, Isle of Rum: a textural and geochemical study of an open-system magma chamber

Published online by Cambridge University Press:  12 November 2008

MARIAN B. HOLNESS  and
BEN WINPENNY
MARIAN B. HOLNESS*
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
BEN WINPENNY
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
*
*Author for correspondence: [email protected]
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Abstract

The Eastern Layered Intrusion of the Rum Central Complex, NW Scotland, comprises 16 macro-units broadly defined by a basal peridotite body overlain by gabbros and troctolites. The local term for the upper plagioclase-bearing cumulates is ‘allivalite’. The Unit 12 allivalite contains five subsidiary peridotite horizons, each continuous on the kilometre scale. Field, textural and geochemical evidence points to the Unit 12 allivalite forming by progressive accumulation of crystals from up to seven separate magma batches, varying from picrite to basalt. The thickness of the magma lens in the sill-like chamber was as low as 30 m during a significant part of the development of the Unit 12 allivalite, and evidence supports one eruption from the chamber during its accumulation.

Keywords

Rumlayered intrusioncumulatetexturetroctolite
Type
Original Article
Information
Geological Magazine , Volume 146 , Issue 3 , May 2009 , pp. 437 - 450
Copyright
Copyright © Cambridge University Press 2008

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