Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Oral

S (Solid Earth Sciences) » S-CG Complex & General

[S-CG61] Ocean Floor Geoscience

Thu. May 24, 2018 9:00 AM - 10:30 AM 302 (3F International Conference Hall, Makuhari Messe)

convener:Kyoko Okino(Atmosphere and Ocean Research Institute, The University of Tokyo), Chairperson:Hanyu Tomoko, Fujii Masakazu(国立極地研究所)

10:00 AM - 10:15 AM

[SCG61-17] Structural development in mantle associated with hydration during transform faulting

*Kakihata Yuki1, Katsuyoshi Michibayashi1, Henry J.B. Dick2 (1.Shizuoka University Graduate School of Science, 2.Woods Hole Oceanographic Institution)

Keywords:transform fault, peridotitic ultramylonite, hydrous shearing

The Southwest Indian Ridge (SWIR) is one of the slowest spreading ocean ridges, where peridotites are partially exposed on the seafloor. We analyzed 7 deformed peridotites derived from the Prince Edward transform fault along the SWIR during PROTEA.5 cruise in 1983. These peridotites show various textures from coarse-granular to ultramylonites and include hydrous minerals such as amphibole. Chemical compositions of olivine and spinel grains are in the range of Olivine-Spinel Mantle Array (OSMA) of Arai (1994) regardless of their textures. Amphibole grains are in the chemical components of tremolite, magnesio-hornblende and pargasite. The occurrence of amphiboles indicates that the peridotites were affected by water under temperature condition up to 800 °C. Olivine crystal-fabrics within deformed amphibole bearing peridotites have B and E types developed under hydrous conditions, whereas olivine fabrics within undeformed amphibole bearing peridotites have A and D types developed under anhydrous conditions. As a consequence, the petrophysical characteristics of peridotites in this study indicate that the uppermost mantle below the Prince Edward transform fault has been locally but intensely hydrated during shearing due to transform movement.