Vesicle layering in solidified intrusive magma bodies: a newly recognized type of igneous structure |
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Authors: | Atsushi Toramaru Akira Ishiwatari Maki Matsuzawa Masaru Nakamura Shoji Arai |
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Institution: | (1) Department of Earth Sciences, Kanazawa University, Kanazawa, 920-11, Ishikawa, Japan. Fax: Japan-762-64-5746, JP |
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Abstract: | We report a novel type of layering structure in igneous rocks. The layering structure in the Ogi picrite sill in Sado Island,
Japan, is spatially periodic, and appears to be caused by the variation in vesicle volume fraction. The gas phase forming
the vesicles apparently exsolved from the interstitial melt at the final stage of solidification of the magma body. We call
this type of layering caused by periodic vesiculation in the solidifying magma body "vesicle layering." The presence of vesicle
layering in other basic igneous bodies (pillow lava at Ogi and dolerite sill at Atsumi, Japan) implies that it may be a fairly
common igneous feature. The width of individual layers slightly, but regularly, increases with distance from the upper contact.
The layering plane is perpendicular to the long axes of columnar joints, regardless of gravitational direction, suggesting
that the formation of vesicles is mainly controlled by the temperature distribution in the cooling magma body. We propose
a model of formation of vesicle layering which is basically the same as that for Liesegang rings. The interplay between the
diffusion of heat and magmatic volatiles in melt, and the sudden vesiculation upon supersaturation, both play important roles.
Received: 15 February 1996 / Accepted: 24 June 1996 |
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Keywords: | Vesicle layering Liesegang ring Igneous layering Bubble nucleation Diffusion |
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