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Field evidence for turbulence during flow of basalt magma through conduits from southwest Mull

Published online by Cambridge University Press:  01 May 2009

I. C. Kille ,
R. N. Thompson ,
M. A. Morrison  and
R. F. Thompson
I. C. Kille
Affiliation:
Department of Geology, Imperial College, Prince Consort Road, London, SW7 2BP, U.K.
R. N. Thompson
Affiliation:
Department of Geology, Imperial College, Prince Consort Road, London, SW7 2BP, U.K.
M. A. Morrison
Affiliation:
Department of Geological Sciences, University of Birmingham, P.O. Box 363, Birmingham B15 2TT, U.K.
R. F. Thompson
Affiliation:
Department of Geology, University of Manchester, Oxford Road, Manchester, M13 9PL, U.K.
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Abstract

The swarm of Palaeocene inclined sheets around Loch Scridain in southwest Mull includes basaltic sheets which contain abundant metasedimentary xenoliths that show evidence for having been partially molten. In contrast with the majority of dyke-like conduits worldwide, which have essentially planar margins, the contact of one of these xenolithic sheets with Moine metasediments is irregular along a segment where it crosses interbedded psammites and pelites. Relatively fusible mica schists have been excavated by the magma, on either side of a massive refractory quartzite horizon. Furthermore, the dolerite of the sheet shows only a slight reduction of grain size, through a zone 0.5 m wide, adjacent to its margin, in contrast with the pronounced marginal chilling which characterizes most intrusions of the Loch Scridain swarm. These field relationships are interpreted as evidence that the basic magma which formed this sheet flowed with local turbulence during its emplacement. The estimated liquidus of the magma (1130 °C at 1 atm) is approximately 200 °C above the solidus of pelitic horizons in the country rock, but far below the solidus of the quartzites.

Type
Articles
Information
Geological Magazine , Volume 123 , Issue 6 , November 1986 , pp. 693 - 697
Copyright
Copyright © Cambridge University Press 1986

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