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Asymmetric extensional structures and their implications for the generation of melanges

Published online by Cambridge University Press:  01 May 2009

D. T. Needham
D. T. Needham
Affiliation:
Department of Earth Sciences, University of London Goldsmiths' College, Rachel McMillan Building, Creek Road, London SE8 3BU, U.K.
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Abstract

Studies of melanges in the Shimanto Belt of southwest Japan have shown that many of the included blocks exhibit asymmetric geometries, similar to boudins and inclusions in medium grade metamorphic rocks which have been subjected to markedly non-coaxial strains. Deformation is accomplished by mesoscopically ductile processes such as pore-pressure-controlled or diffusionally-controlled grain boundary sliding, although localized fracture and cataclasis also occurs. It is suggested that the melanges developed by the propagation of extensional displacement zones, analogous to shear bands, through sandstone beds, so progressively dismembering them. Studies of the detailed internal geometries of melanges along with the deformation mechanisms active during their formation may help resolve the mode of formation of these problematic units.

Type
Articles
Information
Geological Magazine , Volume 124 , Issue 4 , July 1987 , pp. 311 - 318
Copyright
Copyright © Cambridge University Press 1987

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