High temperature acid rocks associated with serpentinite in eastern Quebec

Highly serpentinized alpine-type peridotites frequently have small, relatively acid rock lenses associated with them. Weakly serpentinized or unserpentinized peridotites are usually associated with segregations of olivine gabbro. A study of the acid rocks found in the highly serpentinized peridotite at Asbestos in eastern Quebec indicates that they are metasomatically altered gabbro bodies. The initial alteration was to a biotite-saussurite which was further altered to a microcline-diopside-albite-quartz rock. The degree of alteration was dependent on structural attitude. These rocks represent high temperature alteration in the amphibolite facies which indicates that the serpentinization of the surrounding peridotite has taken place at a higher temperature than is represented by the general level of regional metamorphism, the epidote-amphibolite facies. Chemical evidence suggests that the components which were added to the gabbros may have been derived in part from the peridotite undergoing serpentinization.