Ophiolites have provided the geological community with an opportunity to examine the oceanic crust close at hand. Physical properties of these oceanic rocks can be examined in the laboratory and equated to the geophysical results of oceanic surveys. The Red Mountain ophiolite, South Island, New Zealand, consists of a large fresh ultramafic massif with a layered basic and ultramafic sequence overlying it. The ultramafic massif, Red Mountain, is composed predominantly of tectonized harzburgite. The tectonization has imposed a uniform petrofabric featuring strong olivine crystallographic a maxima which, in 10 field oriented samples, are approximately coincident in direction. The result of these preferred orientations is a strong seismic anisotropy in the samples and in the massif as a whole. The amount of anisotropy, calculated as seven percent for the massif as a whole, is in agreement with values recorded in oceanic seismic refraction surveys.
This strongly suggests that Red Mountain is a coherent obducted section of oceanic upper mantle. Direct comparision of the layered mafic - ultramafic section, the Livingstone Volcanics, with the seismic structure of the oceanic crust is more difficult. Seismic velocities in the variably metamorphosed Livingstone section range from 6.2 km/sec in a metasediment to 7.5 km/sec in a relatively fresh pyroxenite. The velocity studies support the theory that medium grade metamorphism in oceanic rocks will increase their seismic velocities to layer 3 values. The high velocities from the lowermost part of the section are comparable to those reported from basal high velocity zones seen in oceanic studies. The tectonic history of Red Mountain appears complicated. Mafic dikes in the ultramafic upper mantle section indicate a late stage magmatic event, perhaps associated with a marginal basin setting.
Source: Dissertation Abstracts International, Volume: 42-04, Section: B, page: 1364.
Thesis (Ph.D.)--University of Washington, 1981.