Crystal Preferred Orientation of Amphibole Experimentally Deformed in Simple Shear

Abstract:

Seismic anisotropy has been widely observed in the crust and mantle and plays a key role to understand the structure and flow patterns. Although such seismic anisotropy can be explained by the crystal preferred orientation (CPO) of highly anisotropic minerals such as amphibole in the crust, experimental studies on the CPO of amphibole has been very limited. Here we show novel experimental results of simple–shear deformation of amphibolite at high pressure and temperatures (1 GPa, 480–700 °C). The deformed amphibole produced three types of strong CPOs depending on temperature and stress and resulted in a strong seismic anisotropy. Our data open up a new window for understanding the observed seismic anisotropy in the crust. The seismic data obtained from the amphibole CPOs revealed that anomalous seismic anisotropy observed in the deep crust, subducting slab and also at the mantle wedge can be attributed to the CPO of amphibole.