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3581072 
Journal Article 
Brucite as an important phase of the shallow mantle wedge: Evidence from the Shiraga unit of the Sanbagawa subduction zone, SW Japan 
Kawahara, H; Endo, S; Wallis, SR; Nagaya, T; Mori, H; Asahara, Y 
2016 
1 
Lithos
ISSN: 0024-4937 
254 
53-66 
WOS:000375888100004 
Large parts of the shallow mantle wedge are thought to be hydrated due to release of fluids from the subducting slab and serpentinization of the overlying mantle rocks. If serpentinization proceeds under low SiO2 activity, brucite can be a major phase in the low-temperature (<450 degrees C) part of the serpentinized mantle wedge, but only very few natural examples have been documented. A combined petrological, geochemical, and geological study shows that brucite is widely distributed in the wedge mantle-derived Shiraga metaserpentinite body in the Sanbagawa metamorphic belt of SW Japan. Thermodynamic modeling combined with bulk rock composition and point counting indicates that the original fully hydrated shallow parts of the Sanbagawa mantle wedge contained similar to 10-15 vol.% brucite before the onset of exhumation of the Shiraga body and before peak metamorphic conditions. A distinct zone of brucite-free essentially monomineralic antigorite serpentinite occurs limited to a 100-m-thick marginal zone of the body. This indicates a limited degree of Si-metasomatism by slab-derived fluids in the shallow mantle wedge. The presence of brucite may strongly affect the H2O budget and mechanical properties of serpentinite; these should be taken into consideration when examining the behavior of the shallow mantle wedge. (c) 2016 Elsevier B.V. All rights reserved. 
Brucite; Antigorite; Mantle wedge; Serpentinite; Sanbagawa metamorphism; Si metasomatism