These mantle sections consist of harzburgites and dunites that are impregnated by mafic liquids and crosscut by gabbroic and diabase dikes. The mantle rocks are thought to represent the Moho transition zone. This suite of samples has been extensively altered by interaction with seawater. Ultramafics are largely serpentinized.
Gabbroic rocks are strongly hydrated and recrystallized and partly rodingitized.
Most recrystallization occurred under static conditions. Secondary assemblages in the gabbroic rocks provide evidence for at least three successive stages of recrystallization. High-temperature amphiboles are scarce and likely represent an early episode that also crystallized secondary clinopyroxene in veins. The major episode of alteration occurred under greenschist facies conditions and is characterized by coronas of serpentine, tremolite, chlorite, and prehnite. The coronas are contemporaneous with the bulk of serpentinization.