Research Article| April 01, 2008 Porphyroblast rotation versus nonrotation: Conflict resolution! C. Fay; C. Fay 1School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia Search for other works by this author on: GSW Google Scholar T.H. Bell; T.H. Bell 1School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia Search for other works by this author on: GSW Google Scholar B.E. Hobbs B.E. Hobbs 2CSIRO-Exploration and Mining, PO Box 1130, Bentley, Western Australia 6102, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information C. Fay 1School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia T.H. Bell 1School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia B.E. Hobbs 2CSIRO-Exploration and Mining, PO Box 1130, Bentley, Western Australia 6102, Australia Publisher: Geological Society of America Received: 12 Oct 2007 Revision Received: 11 Dec 2007 Accepted: 14 Dec 2007 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2008 Geological Society of America Geology (2008) 36 (4): 307–310. https://doi.org/10.1130/G24499A.1 Article history Received: 12 Oct 2007 Revision Received: 11 Dec 2007 Accepted: 14 Dec 2007 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation C. Fay, T.H. Bell, B.E. Hobbs; Porphyroblast rotation versus nonrotation: Conflict resolution!. Geology 2008;; 36 (4): 307–310. doi: https://doi.org/10.1130/G24499A.1 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 SocietyGeology Search Advanced Search Abstract Data on foliation intersection and/or inflection axes preserved in porphyroblasts (FIAs) indicate that no porphyroblast rotation occurs during ductile deformation relative to spatial coordinates. This contrasts with 99% of investigations of "rigid" objects in non-coaxially deforming media where the objects rotate. When anastomosing shear zone formation around relatively strong objects in a weaker matrix is modeled, no "porphyroblast" rotation occurs. Formation of these anastomosing zones controls the development of this phenomenon, called gyrostasis. If such zones are absent, porphyroblasts rotate. In weak materials the gyrostatic situation arises because the superposition of simple shearing deformation normal to initial coaxial shortening results in only small rotations of principal axes of stress. Since shear zones are controlled by the orientations of principal axes of stress, initial anastomosing zones retain their orientations and positions during subsequent non-coaxial deformation. The porphyroblast is isolated from the embedding non-coaxially deforming matrix, but this material close to the porphyroblast continues to deform coaxially; no local rotation occurs. This has major tectonic significance because, allowing for the effects of rotation due to brittle deformation, porphyroblasts can now be routinely used to access lengthy structural and/or metamorphic histories destroyed in the matrix by reactivation such as movement directions, shear senses, and extended pressure-temperature-time paths. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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