Microstructure of Slate from Lady Loretta, Queensland, Australia

Research Article| January 01, 1975 Microstructure of Slate from Lady Loretta, Queensland, Australia M. A. ETHERIDGE; M. A. ETHERIDGE 1Department of Geology and Mineralogy, University of Adelaide, Adelaide, South Australia 5001, Australia2Present address: (Etheridge) Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia; (Lee) Placer Prospecting (Aust.) Pty. Ltd., P.O. Box 1307, Mt. Isa, Queensland 4825, Australia. Search for other works by this author on: GSW Google Scholar M. F. LEE M. F. LEE 1Department of Geology and Mineralogy, University of Adelaide, Adelaide, South Australia 5001, Australia2Present address: (Etheridge) Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia; (Lee) Placer Prospecting (Aust.) Pty. Ltd., P.O. Box 1307, Mt. Isa, Queensland 4825, Australia. Search for other works by this author on: GSW Google Scholar Author and Article Information M. A. ETHERIDGE 1Department of Geology and Mineralogy, University of Adelaide, Adelaide, South Australia 5001, Australia2Present address: (Etheridge) Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia; (Lee) Placer Prospecting (Aust.) Pty. Ltd., P.O. Box 1307, Mt. Isa, Queensland 4825, Australia. M. F. LEE 1Department of Geology and Mineralogy, University of Adelaide, Adelaide, South Australia 5001, Australia2Present address: (Etheridge) Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia; (Lee) Placer Prospecting (Aust.) Pty. Ltd., P.O. Box 1307, Mt. Isa, Queensland 4825, Australia. Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1975) 86 (1): 13–22. https://doi.org/10.1130/0016-7606(1975)86<13:MOSFLL>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M. A. ETHERIDGE, M. F. LEE; Microstructure of Slate from Lady Loretta, Queensland, Australia. GSA Bulletin 1975;; 86 (1): 13–22. doi: https://doi.org/10.1130/0016-7606(1975)86<13:MOSFLL>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 The preferred orientation of mica in dolomitic slaty siltstone units from Lady Loretta, Queensland, Australia, and its relation to grain size and shape show that the larger, thicker grains have (001) subparallel to bedding, and the thinnest grains have (001) parallel to cleavage. The overall mica orientation depends primarily on bedding-cleavage angle; it bears little relation to bulk composition within the restricted range observed. The shapes of quartz dolomite–rich blebs in two of the specimens have been measured to determine the orientation and shape of their finite strain ellipsoid. The λ1λ2 plane of this ellipsoid is at a low angle to the mica (001) preferred orientation defining the slaty cleavage. This is interpreted to be due either to a difference in strain between the blebs and their matrix, or to the operation of a mica-orienting mechanism that is not related rigorously to the finite strain. Predominantly mechanical orienting mechanisms are considered to be incompatible with the bimodal orientation and grain shape of mica. It is suggested that there was a well-defined preferred orientation in bedding, imposed during diagenesis, and that the cleavage mica grew with a strong preferred orientation during the deformation. A mechanism for this growth control similar to that proposed by Etheridge and others (1974) is favored. 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.