Magnetic, gravity and bathymetry data were collected on an extended
cruise of the R/V Yaquina in 1969. The last set of data was obtained
from those track lines leaving the Panama Basin. The area
covered is mainly the Cocos plate (Molnar and Sykes, 1969). The data
is analyzed and compared with results of previous workers and the
geophysical implications considered.
Generally speaking, from the magnetic part of the data, both
direct and indirect methods show support of Vine and Matthew's
(1963) hypothesis of sea-floor spreading and the subsequent principles
of new global tectonics. The most northern magnetic anomaly profile
across the East Pacific rise (at 18.3°N) shows a spreading rate about
3 cm/yr. and the most southern one (at 12.8°N) shows a rate about
5.2 cm/yr. The Cocos plate has been assumed to move in a northeast-southwest
direction (N30°E to N45°E), and rotate with respect to the
Pacific plate about a pole at 40°N, 110°W with an angular velocity of
19.6x10⁻⁷ deg./yr. (Larson and Chase, 1970). New material comes
up from the west boundary - the East Pacific rise, and the south
boundary - the Galapogos rift, causing the Cocos plate to underthrust
the Americans plate at the middle American arc. Some of the points
of new global tectonics can not be detected from this set of data; further
detailed study of more track lines and sea bottom core samples
are needed. The results of both analytical methods for determining
the magnitude of induced and remanent magnetization in the second
layer shows some consistence with the work of Schaeffer and Schwarz
(1970), and Irving et al. (1970) at the Mid-Atlantic ridge near 45°N, in
which a thinner magnetization layer at the ridge and the attenuation of
magnetization intensity away from the ridge axis are suggested. Free-air
gravity anomaly profiles have been employed to determine the
crustal structure of two sections1 a ridge section at 12.8°N and a
trench section at 14°N. For the ridge section, if the anomalous mantle
was converted from normal mantle, the extension of anomalous mantle
into the normal mantle requires some uplift and/or lateral expansion
in the rise crest area. The tensional configuration suggested in the
trench crustal section agrees with the model proposed by Elsasser
(1968) for the differential movement between two lithospheric blocks.
This work gives some speculations that evidence which supports
the present new global tectonics theory is limited to a certain degree
of accuracy. Further study of the theory based upon physics, its
mechanism, and measurement techniques that would give more reliable
evidence have to be developed before it can be ascertained what
really happens beneath this wild, wild world. / Graduation date: 1971
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29057 |
| Date | 21 April 1971 |
| Creators | Lu, Richard Shih-Ming |
| Contributors | Heinrichs, Donald F. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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