A free-air gravity anomaly map of the area between 10°-17°N and
90°-101°W shows distinctive positive and negative anomalies which
parallel the Tehuatepec Ridge. The positive anomaly approximately
overlies the topographic expression of the ridge. On the wide continental
shelf southeast of the Gulf of Tehuantepec a positive gravity
anomaly with an amplitude in excess of +100 mgal parallels the coast
for most of its length and turns abruptly inland at its northern end.
A crustal and subcrustal cross section constrained by gravity,
magnetic, seismic reflection and seismic refraction data and oriented
normal to the Guatemala continental margin indicates the positive
shelf anomaly is primarily the result of a relatively shallow
2.62 g/cm³ density block which may be continuous with and genetically
similar to the rocks of the Nicoya Complex on the Nicoya Peninsula,
Costa Rica. A crustal and subcrustal cross section normal to the
continental margin off southern Mexico northwest of the Tehuantepec
Ridge shows a shelf structure which is very different from the continental
margin off Guatemala. This suggests different tectonic
interactions at the convergent plate boundaries on opposite sides of
the ridge.
The Tehuantepec Ridge, in a crustal and subcrustal cross section
oriented normal to its trend, is shown to occur at the juncture of
two oceanic crusts of different structure and age. Southeast of the
ridge in the Guatemala Basin the crust is about 9.5 km thick and
northwest of the ridge the crust is about 12 km thick. Hence the
Tehuantepec Ridge is essentially a fracture zone, but because its
orientation is oblique to present plate motions and it is aseismic, it
is concluded to be a relic fracture zone. / Graduation date: 1976
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29141 |
| Date | 17 July 1975 |
| Creators | Woodcock, Stephen Frederick |
| Contributors | Couch, Richard W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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