Gravity, magnetic and seismic data indicate that the oceanic
crust is 9.7 km thick west of the Continental Borderland. The top
of the mantle is about 12 km deep under the Borderland, and deepens
to 27 km beneath the Peninsular Ranges of Baja California. The
mantle is about 20 km below the surface of the Imperial Valley and
deepens to 27 km under the area east of the Imperial Valley.
The age of the youngest detectable remnant magnetic anomaly
over the oceanic crust is about 16.5 million years at 21.3°N Lat.
and decreases to the south. A magnetic anomaly expected along the
continuation of the San Benito Fault Zone is not detected by this study.
A gravity low along the base of the Patton Escarpment is at least
partially the result of a buried trench-like depression. In the vicinity
of 31.3°N Lat., 119.3°W Long. this depression is filled with 2 km
of sediments.
The geophysical and geological data are interpreted as indicating
a 6 km thick section of Franciscan rocks that extends from the west
edge of the Borderland to the Coronado Escarpment. Magnetic data
suggest that an ophiolite may be present within or on top of the Franciscan
rocks.
Several of the ridges in the Borderland have cores of high density
rocks which are interpreted as intrusives. The area just south of the
San Clemente basin has an anomalously thin upper crust. The gross
crustal structure of this region is comparable to the Imperial Valley
region and may represent a former site of crustal rifting which
occurred when the East Pacific Rise was subducted under this part of
the North American plate. North of the Santo Tomas Fault Zone are
several basins filled with more than 3 km of sediments, but south of
this fault zone the sediment cover is discontinuous and generally less
than 2 km thick. / Graduation date: 1978
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29203 |
| Date | 16 December 1977 |
| Creators | Plawman, Thomas Leon |
| Contributors | Couch, Richard W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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