Amphibole fabric formation during diffusion creep and the rheology of shear zones

Abstract

Research Article| June 01, 2014 Amphibole fabric formation during diffusion creep and the rheology of shear zones A.J. Getsinger; A.J. Getsinger * Department of Geological Sciences, Brown University, Box 1846, 324 Brook Street, Providence, Rhode Island 02912, USA *E-mails: Amanda_Getsinger@brown.edu; Greg_Hirth@brown.edu. Search for other works by this author on: GSW Google Scholar G. Hirth G. Hirth * Department of Geological Sciences, Brown University, Box 1846, 324 Brook Street, Providence, Rhode Island 02912, USA *E-mails: Amanda_Getsinger@brown.edu; Greg_Hirth@brown.edu. Search for other works by this author on: GSW Google Scholar Geology (2014) 42 (6): 535–538. https://doi.org/10.1130/G35327.1 Article history received: 24 Nov 2013 rev-recd: 19 Mar 2014 accepted: 21 Mar 2014 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 A.J. Getsinger, G. Hirth; Amphibole fabric formation during diffusion creep and the rheology of shear zones. Geology 2014;; 42 (6): 535–538. doi: https://doi.org/10.1130/G35327.1 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 We conducted experiments to examine the effect of amphibole-forming hydration reactions on mineral fabric development and the strength of mafic rocks. Both hydrostatic and general shear deformation experiments were conducted on powdered basalt with added water at lower continental crust conditions (800 °C, 1 GPa). Amphibole that formed under hydrostatic conditions exhibits a random lattice-preferred orientation (LPO). In contrast, amphibole formed during deformation exhibits both a strong shape-preferred orientation (SPO) and LPO with a [001] maximum aligned subparallel to the shear direction. Plagioclase in both hydrostatic and deformed samples shows a very weak to random LPO. At low effective strain rates (10−5 s−1 to 10−6 s−1), the stress exponent is ≈1–1.5, consistent with deformation accommodated by diffusion creep. The correlation of the SPO and LPO coupled with the rheological evidence for diffusion creep indicates that the amphibole fabric results from oriented grain growth and rigid grain rotation during deformation. The experimentally produced fabrics are strikingly similar to those observed in amphibolite-grade natural shear zones, supporting interpretations that such rocks deform by diffusion creep. In addition, the rheology of the fine-grained experimental amphibolite is comparable to that predicted using flow laws for wet anorthite. Thus, both our experiments and field analyses indicate that wet plagioclase rheology provides a good constraint on the strength of hydrated lower crust. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.