High-level peperitic sills in the English Lake District: Distinction from block lavas, and implications for borrowdale volcanic group stratigraphy
Article first published online: 30 APR 2007
Copyright © 1988 John Wiley & Sons, Ltd
Volume 23, Issue 2, pages 171–187, April/June 1988
How to Cite
Branney, M. J. and Suthren, R. J. (1988), High-level peperitic sills in the English Lake District: Distinction from block lavas, and implications for borrowdale volcanic group stratigraphy. Geol. J., 23: 171–187. doi: 10.1002/gj.3350230206
- Issue published online: 30 APR 2007
- Article first published online: 30 APR 2007
- Manuscript Revised: 15 NOV 1987
- Manuscript Received: 20 JUL 1987
- Block lavas;
- English Lake District
Criteria by which such sills can be distinguished from block lavas include discordance and fault-controlled geometry, vesiculation and homogenization of sediments adjacent to upper contacts, and the presence of pillows or peperites at upper contacts. Because sills do not always show these characteristics in the field, an extrusive origin for a sheet should be demonstrated and not assumed. However, it is not always possible to make the distinction, in which case the non-genetic term sheet can be usefully applied.
Field studies suggest that a substantial part of the Borrowdale Volcanic Group is composed of sills. Thus previously erected lithostratigraphic schemes may not correctly indicate the sequence of magmatic events, and the correlation of locally defined stratigraphies will not be possible until the regional importance of high-level intrusive bodies has been established.