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Seismic properties and petrofabrics of ultramafic and mafic rocks from the Red Mountain ophiolite, New Zealand [microform]
Bib ID 3287406
Format MicroformMicroform, BookBook
Author
Wilkens, Roy Henry
 
Description 216 p. 
Summary

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.

Notes

(UnM)AAI8121262

Source: Dissertation Abstracts International, Volume: 42-04, Section: B, page: 1364.

Thesis (Ph.D.)--University of Washington, 1981.

Reproduction Microfiche. Ann Arbor, Mich.: University Microfilms International. 
Subjects Geology.
Other authors/contributors University of Washington
000 02729nam a2200241   4500
001 3287406
005 20041008105859.0
008 040506s1981    miu|||||bm||||||| ||eng d
019 1 |a26244671
040 |aUnM|beng|cUnM|dOCoLC
100 1 |aWilkens, Roy Henry.
245 1 0 |aSeismic properties and petrofabrics of ultramafic and mafic rocks from the Red Mountain ophiolite, New Zealand|h[microform].
300 |a216 p.
500 |a(UnM)AAI8121262
500 |aSource: Dissertation Abstracts International, Volume: 42-04, Section: B, page: 1364.
502 |aThesis (Ph.D.)--University of Washington, 1981.
520 |aOphiolites 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.
520 |aThis 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.
533 |aMicrofiche.|bAnn Arbor, Mich.:|cUniversity Microfilms International.
650 4 |aGeology.
710 2 |aUniversity of Washington.
773 0 |tDissertation Abstracts International|g42-04B.
984 |aANL|cmc 252 81-21262
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