Deformation of a Slaty, Lapillar Tuff in the Lake District, England

Research Article| April 01, 1970 Deformation of a Slaty, Lapillar Tuff in the Lake District, England G OERTEL G OERTEL Department of Geology, University of California, Los Angeles, California 90024 Search for other works by this author on: GSW Google Scholar Author and Article Information G OERTEL Department of Geology, University of California, Los Angeles, California 90024 Publisher: Geological Society of America Received: 19 May 1969 Accepted: 24 Oct 1969 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1970, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1970) 81 (4): 1173–1188. https://doi.org/10.1130/0016-7606(1970)81[1173:DOASLT]2.0.CO;2 Article history Received: 19 May 1969 Accepted: 24 Oct 1969 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation G OERTEL; Deformation of a Slaty, Lapillar Tuff in the Lake District, England. GSA Bulletin 1970;; 81 (4): 1173–1188. doi: https://doi.org/10.1130/0016-7606(1970)81[1173:DOASLT]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract An andesite tuff of Ordovician age from the Lake District, England, contains accretionary (hailstone) lapilli. These originally spherical bodies allow a tentative analysis of their history of deformation, at least for the single, isolated point from which a sample was taken. The lapilli were first deformed into oblate spheroids by compaction which shortened them vertically 53 percent, then the bedding plane was tilted 21° to the south-southwest. Thereafter the rock was converted to a chlorite-muscovite slate, shortened 50 percent along a near-horizontal north-south line, lengthened 100 percent near vertically, and left unchanged along the east-west horizontal. The direction of greatest shortening is normal to the cleavage, that of greatest lengthening parallel to a lineation in the cleavage plane. An X-ray diffraction pole-figure from three mutually perpendicular sections scanned in transmission indicates a preferred orientation of 9 times random of the basal planes of chlorite parallel to the cleavage plane. Preferred orientation of muscovite is similar to that of chlorite. Passive rotation of originally random platelets during the tectonic strain could explain preferred orientation of 8 times random; preferential post-tectonic growth of platy minerals parallel to their base, more often stopped by impingement on other grains if grains form large angles with the cleavage, may have enhanced the orientation.Folds with axial surfaces different from the plane of slaty cleavage were observed 350 m from the sample point. If one assumes, somewhat tenuously, that the strain leading to slaty cleavage was fairly homogeneous over this distance and was the last strain to affect the rocks, then the shape of the folds before the cleavage episode can be reconstructed. Such a reconstruction of one fold and of its pre-cleavage fold axis and axial plane gives an idea of the shape of this fold as it may have existed after the pre-Bala folding episode and before the final deformation sometime during the Devonian Period. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.