Kinematic vorticity analysis and evolving strength of mylonitic shear zones: New data and numerical results

Abstract

Research Article| December 01, 2009 Kinematic vorticity analysis and evolving strength of mylonitic shear zones: New data and numerical results Scott E. Johnson; Scott E. Johnson 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Search for other works by this author on: GSW Google Scholar Hendrik J. Lenferink; Hendrik J. Lenferink 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Search for other works by this author on: GSW Google Scholar Jeffrey H. Marsh; Jeffrey H. Marsh 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Search for other works by this author on: GSW Google Scholar Nancy A. Price; Nancy A. Price 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Search for other works by this author on: GSW Google Scholar Peter O. Koons; Peter O. Koons 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Search for other works by this author on: GSW Google Scholar David P. West, Jr. David P. West, Jr. 2Department of Geology, Middlebury College, Middlebury, Vermont 05753, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Scott E. Johnson 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Hendrik J. Lenferink 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Jeffrey H. Marsh 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Nancy A. Price 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA Peter O. Koons 1Department of Earth Sciences, University of Maine, Orono, Maine 04469, USA David P. West, Jr. 2Department of Geology, Middlebury College, Middlebury, Vermont 05753, USA Publisher: Geological Society of America Received: 11 Mar 2009 Revision Received: 06 Jul 2009 Accepted: 07 Jul 2009 First Online: 03 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2009 Geological Society of America Geology (2009) 37 (12): 1075–1078. https://doi.org/10.1130/G30227A.1 Article history Received: 11 Mar 2009 Revision Received: 06 Jul 2009 Accepted: 07 Jul 2009 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Scott E. Johnson, Hendrik J. Lenferink, Jeffrey H. Marsh, Nancy A. Price, Peter O. Koons, David P. West; Kinematic vorticity analysis and evolving strength of mylonitic shear zones: New data and numerical results. Geology 2009;; 37 (12): 1075–1078. doi: https://doi.org/10.1130/G30227A.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 The kinematic vorticity number is an important quantity in structural geology and tectonics, giving a nonlinear ratio of simple shear to pure shear deformation. We use natural observations and numerical models to show how rigid clast methods for determining the kinematic vorticity number (Wk) are compromised where strain localization occurs at the matrix-clast interface. Our numerical results show that the critical shape factor cutoff between permanently rotating and stable clasts, used to determine Wk, is highly sensitive to coupling between the clast and the matrix. This finding provides an elegant explanation for the fact that rigid clast methods tend to underestimate Wk relative to other methods. We present numerically determined envelopes for clast behavior across a range of kinematic vorticity numbers, clast shape factors, and matrix-clast coupling. Our numerical models show that the shape-preferred orientations of feldspar clasts trend toward the positions of mica fish with increasing localization at the clast boundary, suggesting that mica fish behave as highly lubricated clasts. Our data and numerical results show that the clast-matrix interface may be several orders of magnitude weaker than the surrounding matrix and that weak interfaces can lead to a marked drop in the bulk shear strength of faults and shear zones. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.