Mantle earthquakes frozen in mylonitized ultramafic pseudotachylytes of spinel-lherzolite facies

Abstract

Research Article| August 01, 2008 Mantle earthquakes frozen in mylonitized ultramafic pseudotachylytes of spinel-lherzolite facies T. Ueda; T. Ueda * 1Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan *E-mail: t_ueda@kueps.kyoto-u.ac.jp Search for other works by this author on: GSW Google Scholar M. Obata; M. Obata 1Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kitashirakawa Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan Search for other works by this author on: GSW Google Scholar G. Di Toro; G. Di Toro 2Dipartimento di Geoscienze, Padova University, Via Giotto 1, 35317 Padova, Italy, and Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, 00143 Rome, Italy Search for other works by this author on: GSW Google Scholar K. Kanagawa; K. Kanagawa 3Department of Earth Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba City 263-8522, Japan Search for other works by this author on: GSW Google Scholar K. Ozawa K. Ozawa 4Department of Earth and Planetary Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (8): 607–610. https://doi.org/10.1130/G24739A.1 Article history received: 03 Jan 2008 rev-recd: 19 Apr 2008 accepted: 22 Apr 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation T. Ueda, M. Obata, G. Di Toro, K. Kanagawa, K. Ozawa; Mantle earthquakes frozen in mylonitized ultramafic pseudotachylytes of spinel-lherzolite facies. Geology 2008;; 36 (8): 607–610. doi: https://doi.org/10.1130/G24739A.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 report a new type of ultramafic pseudotachylyte that forms a fault- and injection-vein network hosted in the mantle-derived Balmuccia peridotite (Italy). In the fault vein the pseudotachylyte is now deformed and recrystallized into a spinel-lherzolite facies ultramylonite, made of a fine (<2 μm) aggregate of olivine, orthopyroxene, clinopyroxene, and spinel, with small amounts of amphibole and dolomite. Electron backscattered diffraction study of the ultramylonite shows a clear crystallographic preferred orientation (CPO) of olivine. The fault vein pseudotachylyte overprints a spinel-lherzolite facies amphibole-bearing mylonite, indicating that shear localization accompanying chemical reaction had taken place in the peridotite before seismic slip produced frictional melting. The occurrence of amphibole in the host mylonite and that of dolomite as well as amphibole in the matrices of ultramylonite and pseudotachylyte may indicate that fluid was present and had evolved in its composition from H2O-rich to CO2-rich during ductile deformation with metamorphic reactions, which may account for the observed rheological transition from ductile to brittle behavior. The spinel-lherzolite facies assemblage in mylonites, P-T estimations from pyroxene geothermometry and carbonate reactions, and the type of olivine CPO in deformed pseudotachylyte indicate that both the preseismic and the postseismic ductile deformations occurred at ~800 °C and 0.7–1.1 GPa. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.