Discussion on “Coesite-bearing eclogite breccia: implication for coseismic ultrahigh-pressure metamorphism and the rate of the process” by Yang et al. (Contrib. Mineral. Petrol., 2014a, 167: 1013)
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- Ji, S. Contrib Mineral Petrol (2015) 170: 1. doi:10.1007/s00410-015-1154-3
Recently, Yang et al. (Contrib Mineral Petrol 167:1013, 2014a) proposed that “cataclasites,” “breccias” and “pseudotachylytes” of eclogites at Yangkou in the Chinese Sulu UHP metamorphic belt are formed by “a compression stress wave of earthquake.” They suggested that the intergranular coesite resulted from a rapid cooling from about 700 °C to below 375–400 °C and a “sudden pressure release of seismic wave” from 3.3 to 1.2 GPa in some hours. However, the earthquake-induced UHP metamorphism under fluid-deficient conditions, proposed by these authors, remains inconclusive and inconsistent with the available data from the UHP metamorphic belt. The coesite inclusions within garnet, zircon and omphacite, and intergranular coesite grains between these minerals can be preserved by the presence of the pressure vessel effect, the lack of fluid infiltration, and the presence of a low-temperature and nonhydrostatic deformation environment during rapid exhumation.