HR: 16:45h
AN: T44B-04    [Abstracts]
TI: Frictional Melting of Syenite in High-velocity Rotary Shear Experiments: `Mingling' of Molten Layers and Slip Localization
AU: * Ree, J
EM: reejh@korea.ac.kr
AF: Department of Earth and Environmental Sciences, Korea University, Anam-dong, Seoul, 136-701, Korea, Republic of
AU: Han, R
EM: rhhan@korea.ac.kr
AF: Department of Earth and Environmental Sciences, Korea University, Anam-dong, Seoul, 136-701, Korea, Republic of
AU: Kim, J
EM: mdew2000@korea.ac.kr
AF: Department of Earth and Environmental Sciences, Korea University, Anam-dong, Seoul, 136-701, Korea, Republic of
AU: Shimamoto, T
EM: shima007@hiroshima-u.ac.jp
AF: Department of Earth and Planetary Systems Science, Hiroshima University, Higashi- Hiroshima, Hiroshima, 739-8526, Japan
AB: We report a mingling behavior of granitic and andesitic melts produced by frictional heating in simulated faults of a syenite using a high-velocity rotary shear testing apparatus at Kyoto University. The syenite (so-called larvikite) is composed of perthitic alkali feldspar (~80%), mafic minerals (~15%), apatite (2 - 3%) and nepheline (1 - 2%). The mafic minerals (clinopyroxene, olivine, titanomagnetite and biotite) and apatite occur as aggregates, although there are some isolated smaller grains of titanomagnetite, biotite and apatite within feldspars. The friction experiments were conducted at seismic slip rates of 0.31 to 1.13 m/s, normal stresses of 5.2 or 18.3 MPa and at room temperature. At the onset of the shearing, the first peak friction (μ = 0.35 - 0.66) was followed by a transient slip weakening. Then with further slip, the friction coefficient increased to a second peak value (0.25 - 0.77) followed by a final weakening with steady-state friction coefficient of 0.15 - 0.35. We also terminated the shearing experiments during the first transient weakening and second strengthening to observe microstructural developments, and found that the first transient weakening and second strengthening correspond to gouge-generating wear and patchy melting, respectively. The final weakening was induced by the development of molten layer(s) along the slip zone. These mechanical and microstructural evolutions are similar to those of high-velocity friction experiments on gabbro (Hirose and Shimamoto, 2005, JGR, B05202). The ˇ®bulk' temperature of the slip zone measured by a radiation thermometer reached up to about 1250°C. However, partially molten olivine (Fo₄₀), clinopyroxene (augite) and titanomagnetite in pseudotachylyte (PT) band suggest that the local temperature was at least about 1500°C. The PT band along the slip zone consists of two parallel glass layers, one granitic (25 - 55 μm thick) and the other andesitic (25 - 100 μm thick) layers, or three glass layers in which the andesitic layer is mantled by granitic layers. The granitic glass was produced probably by friction between feldspars, while the andesitic glass was likely to be formed by friction between feldspars and mafic minerals. With the layered configuration of molten materials with different viscosity, we suspect that slip might be localized along the less viscous andesitic layer. However, it is not clear at present why the two molten layers were juxtaposed rather than mechanically mixed at seismic slip rates.
DE: 3902 Creep and deformation
DE: 5112 Microstructure
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8012 High strain deformation zones
DE: 8034 Rheology and friction of fault zones (8163)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting