Abstract

Accepting that alpine serpentines are tectonically emplaced in the solid state, the writer suggests that they may be fragments of the sea floor derived from the Oceanic Layer. This concept is based on the writer's belief that eugeosynclinal graywackes may be equated with modern continental-rise turbidite prisms which are laid down on the deep-sea floor, abutting and overlapping, in part, the continental slope. When the sea floor thrusts toward the continent, the continental-rise prism is folded into a eugeosynclinal prism. The Franciscan graywackes prism of the California Coast Range would be an example. Pods of serpentine derived from the sea-floor sima underlying the eugeosyncline would be caught up in this folding, along with some deeper sub-M discontinuity ultramafic mantle rock. It is further supposed that the spilite-keratophyre suite characteristic of eugeosynclines is laid down in the deep ocean, Na metasomatism being caused by sea-water contact. On the floor of the open sea, away from the continental-rise turbidites, Layer 2 of sea-floor seismology probably is made up of spilite plus lithified eupelagic sediments altered to chert, ironstone, red argillite, and carbonate rock. This view has implications for the Mohole project.

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