Creep cavitation bands control porosity and fluid flow in lower crustal shear zones

Abstract

Research Article| March 01, 2015 Creep cavitation bands control porosity and fluid flow in lower crustal shear zones Luca Menegon; Luca Menegon 1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth PL4 8AA, UK Search for other works by this author on: GSW Google Scholar Florian Fusseis; Florian Fusseis 2School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, UK Search for other works by this author on: GSW Google Scholar Holger Stünitz; Holger Stünitz 3Department of Geology, University of Tromsø, 9037 Tromsø, Norway Search for other works by this author on: GSW Google Scholar Xianghui Xiao Xianghui Xiao 4Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Luca Menegon 1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth PL4 8AA, UK Florian Fusseis 2School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, UK Holger Stünitz 3Department of Geology, University of Tromsø, 9037 Tromsø, Norway Xianghui Xiao 4Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA Publisher: Geological Society of America Received: 25 Sep 2014 Revision Received: 15 Dec 2014 Accepted: 17 Dec 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (3): 227–230. https://doi.org/10.1130/G36307.1 Article history Received: 25 Sep 2014 Revision Received: 15 Dec 2014 Accepted: 17 Dec 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 Luca Menegon, Florian Fusseis, Holger Stünitz, Xianghui Xiao; Creep cavitation bands control porosity and fluid flow in lower crustal shear zones. Geology 2015;; 43 (3): 227–230. doi: https://doi.org/10.1130/G36307.1 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 Shear zones channelize fluid flow in Earth’s crust. However, little is known about deep crustal fluid migration and how fluids are channelized and distributed in a deforming lower crustal shear zone. This study investigates the deformation mechanisms, fluid-rock interaction, and development of porosity in a monzonite ultramylonite from Lofoten, northern Norway. The rock was deformed and transformed into an ultramylonite under lower crustal conditions (temperature = 700–730 °C, pressure = 0.65–0.8 GPa). The ultramylonite consists of feldspathic layers and domains of amphibole + quartz + calcite, which result from hydration reactions of magmatic clinopyroxene. The average grain size in both domains is <25 μm. Microstructural observations and electron backscatter diffraction analysis are consistent with diffusion creep as the dominant deformation mechanism in both domains. Festoons of isolated quartz grains define C′-type bands in feldspathic layers. These quartz grains do not show a crystallographic preferred orientation. The alignment of quartz grains is parallel to the preferred elongation of pores in the ultramylonites, as evidenced from synchrotron X-ray microtomography. Such C′-type bands are interpreted as creep cavitation bands resulting from diffusion creep deformation associated with grain boundary sliding. Mass-balance calculation indicates a 2% volume increase during the protolith-ultramylonite transformation, which is consistent with synkinematic formation of creep cavities producing dilatancy. Thus, this study presents evidence that creep cavitation bands may control deep crustal porosity and fluid flow. Nucleation of new phases in creep cavitation bands inhibits grain growth and enhances the activity of grain size–sensitive creep, thereby stabilizing strain localization in the polymineralic ultramylonites. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.