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Magma flow regimes in sills deduced from Ar isotope systematics of host rocks

Wartho, Jo-Anne; Kelley, Simon and Blake, Stephen (2001). Magma flow regimes in sills deduced from Ar isotope systematics of host rocks. Journal of Geophysical Research: Solid Earth, 106(B3) pp. 4017–4035.

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The best place to seek evidence of the style of past magma flow through a conduit is in the country rock. Heat flow has been studied in country rock adjacent to two Tertiary dolerite sills intruding the Caledonian schists and quartzites, on the Isle of Mull, Scotland, Radiogenic Ar-40 loss within mica grains in the thermal aureoles of the intrusions has been measured at high spatial resolution using the Ultra-Violet Laser Ablation Micro-Probe, to discriminate between a history of prolonged magma flow, a history of conductive cooling following laminar flow, and instantaneous emplacement of the intrusions. The Ar-40/Ar-39 mica data and thermal modeling suggest that a prolonged period of magma flow of 3-5 months resulted in extensive argon loss from the micas, country rock melting, and mineral breakdown adjacent to a 6-m sill. These features were absent from the wall rocks of a smaller 2.7-m-thick sill, which exhibited even less argon loss than might have been predicted for an instantaneous intrusion. If the heat loss from the 6-m sill observed in one locality had been repeated along its length, it would have formed an important magma conduit to the Mull volcano, but dolerite is not a common flow composition on Mull. If on the other hand, the heat loss from the sill varies along strike, it constitutes strong evidence for channelling and heterogeneous flow within the sill.

Item Type: Journal Item
ISSN: 2169-9356
Keywords: Geochemistry; Geochronology; Instruments and techniques; Volcanology; Magma migration; Physics and chemistry of magma bodies
Academic Unit/School: Learning and Teaching Innovation (LTI) > Institute of Educational Technology (IET)
Learning and Teaching Innovation (LTI)
Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 4220
Depositing User: Simon Kelley
Date Deposited: 04 Jul 2006
Last Modified: 07 Dec 2018 08:56
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