Formation and maintenance of shear zones

Research Article| February 01, 2006 Formation and maintenance of shear zones Caleb W. Holyoke, III; Caleb W. Holyoke, III 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA Search for other works by this author on: GSW Google Scholar Jan Tullis Jan Tullis 1Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA Search for other works by this author on: GSW Google Scholar Geology (2006) 34 (2): 105–108. https://doi.org/10.1130/G22116.1 Article history received: 31 Jul 2005 rev-recd: 10 Oct 2005 accepted: 12 Oct 2005 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Caleb W. Holyoke, Jan Tullis; Formation and maintenance of shear zones. Geology 2006;; 34 (2): 105–108. doi: https://doi.org/10.1130/G22116.1 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 processes that initiate and maintain prograde ductile shear zones are not well understood. We have performed shear experiments (γ = 1 to 3) on a fine-grained (100– 150 μm) gneiss (59% quartz, 28% plagioclase, 13% aligned but not interconnected biotite) to determine the evolution of deformation mechanisms that produce dramatic strain weakening and localization, at conditions (1.5 GPa, 800 °C, \({{{γ}}}\) = 2 × 10−5/s) where pure quartz aggregates deform homogeneously by dislocation creep. Initial yield occurs where stress concentrations at the tips of weak biotite grains produce semibrittle deformation in intervening quartz or plagioclase, allowing local biotite interconnection by slip on (001) and initiating strain weakening. After yield, the interconnected biotites kink and thus strengthen, but the highly strained parts of grains react to a fine-grained, mixed-phase assemblage which deforms by grain-size–sensitive creep, allowing further strain weakening and localization. At γ = 3.3, the strain and strain rate in the ∼100-μm-thick shear zone are 100 times that of the enclosing host rock, similar to the localization observed in natural shear zones. Thus, the processes that initiate strain localization are not necessarily the same as those that preserve the weak shear zone, and once formed, a shear zone may be permanently weakened. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.