Gravity and seismic data obtained by the geophysical group at
Oregon State University on the R/V YAQUINA during 1969, 1971, and
1973 plus other available data over the area just west of Nicaragua
and Costa Rica indicate the tectonic complexity of the region. Gravity
measurements show negative free-air anomalies over the Middle
America Trench and the continental shelf of Nicaragua with values as
low as -120 mgal and -90 mgal respectively. An outer shell gravity
high of +35 mgal occurs between the lows. A large positive anomaly
attaining values as high as +110 mgal is associated with the Nicoya
Complex, a late Mesozoic assemblage, on the Nicoya Peninsula, Costa
Rica. Continuous seismic reflection records acquired along the continental
shelf of Nicaragua and Costa Rica indicate a large sediment-filled
basin off the coast of Nicaragua coincident with the large negative
gravity anomaly on the shelf. Free-air gravity anomalies and seismic
reflection profiles suggest an offshore continuation of the Nicoya
Complex. Two crustal and subcrustal cross sections of the continental
margin of Nicaragua show a large anticlinal structure near the surface
of the outer shelf. This structure and an underlying layer are postulated
to be marine sediments and basalts similar to those of the
Nicoya Complex. The cross sections suggest a ruptured oceanic
layer beneath the trench.
Imbricate thrusting of oceanic crust along the continental slope
is postulated as the mechanism of formation of the continental slope
and shelf, and hence the Nicoya Complex of Costa Rica. This model
has to be modified for southern Costa Rica where the Cocos Ridge
terminates the Middle America Trench. The present elevation of the
Nicoya Complex onshore may be attributed to imbricate thrusting and
concurrent uplift of the shelf by the Cocos Ridge during subduction. / Graduation date: 1976
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29147 |
| Date | 24 September 1975 |
| Creators | Victor, Linda |
| Contributors | Couch, Richard W. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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