Serpentinites and related rocks of Anglesey

A series of ultramafic igneous bodies occurs in the Pre-Cambrian (Monian) metasedimentary rocks of Anglesey. The latter are finely-banded semi-pelites of greenschist facies and have undergone two main phases of deformation. Most of the structures are weakly developed near the intrusions where an irregular zone of epidote hornfels was produced. The ultramafic bodies were emplaced as peridotite magmas immediately prior to D. Thorough serpentinization followed and the resulting serpentinites have a variety of appearances. A later carbonatization was intense in places. The structures and textures of the intrusive rocks can be correlated with regional events. Various melagabbroic rocks, now highly altered, may be comagmatic with the peridotite although intruded rather later.