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Ptygmatic Structures and their Formation

Published online by Cambridge University Press:  01 May 2009

Gilbert Wilson
Gilbert Wilson
Affiliation:
Department of Geology, Imperial College, London, S.W. 7.
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Abstract

The conditions under which ptygmatic veins develop occur when the country-rock—as in a granitized area—is locally less competent or more yielding than quartzo-felspathic magma which may intrude it. Veins therefore which are being driven forward by pressure from behind, will buckle plastically if they encounter a resistance during injection, and a succession of such buckles will produce a typical ptygmatic vein. The amplitudes of the flexures so formed depend on the relative physical states of the vein and host-rock; so for any particular vein there is usually a more or less constant size for the tortuosities developed. The mechanism explains several features observed in examples of ptygmatic veins, and has been reproduced experimentally in the laboratory. The contortions are therefore not necessarily due to the deformation of the veins by post-injection flowage or tectonic movements of the country-rock.

Type
Articles
Information
Geological Magazine , Volume 89 , Issue 1 , February 1952 , pp. 1 - 21
Copyright
Copyright © Cambridge University Press 1952

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