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Felsic rocks are minor in abundance but occur ubiquitously in International Ocean Discovery Program Hole U1473A, Southwest Indian Ridge. The trace element abundances of high-Ti brown amphibole, plagioclase, and zircon in veins, as well as the presence of myrmekitic texture in the studied felsic rocks support crystallization origin from highly-evolved melts, probably controlled by fractional crystallization. Based on geochemical criteria and texture of the mineral assemblage in felsic rocks and their relationship with host gabbros, they can be divided into three types: (1) Felsic rock with sharp boundaries is formed when felsic melt intrudes into fractures of host gabbros, resulting in minimal interaction between the melt and the wall minerals. (2) Replacive felsic rock, which is characterized by a pseudomorphic replacement of minerals in the host gabbro. This vein type is caused by the replacement of the host mineralogy by minerals in equilibrium with the felsic melts. (3) Felsic rock with diffused boundaries is formed either by infiltration of felsic melt into the solidifying gabbro body or crystallization of interstitial melts. Infiltration modes of felsic melts are likely controlled by the temperature condition of the cooling host gabbros.

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We report on the evidence of the pulverization in a deep-seated meta-anorthosite in the Eidsfjord shear zone, Vesterålen, northern Norway. Some plagioclase porphyroclasts comprise a few large relict clasts and many fine grains that preserve the outlines of the original grains. The fine-grained plagioclase does not show any plastic-deformation microstructures and has strong crystallographic preferred orientations, which are inherited from the twinned porphyroclast. Misorientation-axis distributions indicate that the grains have rotated randomly, so that the misorientation axes are not aligned with either the crystallographic or kinematic axes. The observed grain-size distribution has a fractal dimension, suggesting their fracturing/ fragmentation origin. The microstructures are characterized by the fracturing/fragmentation with a very low shear strain, indicating that it may be associated with pulverization at~20-25 km depth.

Foliated antigorite serpentinites are contributing to seismic anisotropy in subduction zones. However, uncertainty remains regarding the development of antigorite crystal preferred orientations (CPO). This study analyzes the CPOs of antigorite and olivine in variably serpentinized samples of antigorite serpentinite from three localities in Southwest Japan, using U-stage, EBSD, and synchrotron X-rays. In all samples (010) poles show a maximum parallel to the lineation, and (001) poles concentrate normal to the foliation with a partial girdle about the lineation. (100) poles are less distinct and scatter widely. The three measurement methods give similar results, though orientation distributions from X-ray analysis which averages over larger sample volumes are more regular and weaker than U-stage and EBSD which focuses on local well-crystallized grains. In olivine-bearing serpentinite, the olivine CPO does not appear to control the antigorite CPO, though there are some topotactic relationships. The antigorite CPO formed contemporaneously with serpentinization and shear deformation. Based on our analyses, in a subduction zone mantle wedge, the (010) pole of antigorite is parallel to the direction of the subduction, and (001) lattice planes are parallel to the interface of the subducting oceanic plate. By averaging single crystal elastic properties over orientation distributions wave velocities have been calculated. Fast P velocities are parallel to the subduction direction and slow velocities are perpendicular to the subducting plate with an anisotropy of 10-15%.