GEOLOGIC OBSERVATIONS OF THE NORTHERN BOUNDARY OF THE
CARIBBEAN PLATE ACROSS CENTRAL AMERICA
AS SEEN BY SEASAT AND SIR-A
Ph. REBILLARD *, T. DIXON, T. FARR
Jet Propulsion Laboratory
MS 185/701, 4800 Oak Grove Drive
Pasadena, CA 91109, USA
* National Research Council! Research Associate
ABSTRACT
A mosaic of four digitally correlated Seasat Synthetic Aperture Radar images
(rev 759) over Central America covers the northwestern Caribbean Plate
boundary. The radar data extend from the Amatique Bay (Golfo de Honduras) in
the northeast to the Pacific Ocean (Puenta Remedios) in the southwest. Space
Shuttle Imaging Radar (SIR-A) data-take 18 overlaps the main part of the
Seasat mosaic. SIR-A data permit more observations over the Central American
Cordillera, where strong layover limited the amount of information obtained by
Seasat.
The radar coverage delineates the major strike-slip faults of the
region (Cuilco-Chixoy-Polochic, Motagua and Jocotan) which have acted as the
Caribbean-Americas plate boundary. It also discriminates volcanic terranes
related to subduction of the Cocos Plate under the Caribbean Plate.
Within pumice fields of the Tertiary volcanic belt the use of two
Seasat look directions (rev 759 and rev 1211) in conjuction with SIR-A data
allows some rock discrimination. Further work on texture using Fourier
spectra is presented separately (Farr et al., 1982).
GEOLOGICAL SETTING
The study area is located in Guatemala and extends from the Amatique Bay in
the northeast to the Pacific Ocean in the southwest. It includes the four
geological provinces. From north to south , they are: the Peten Lowland and
the Chapayal Basin, the Central American Cordillera (which forms the axis of
the country), the Volcanic Belt and the Pacific Coastal Plain (Weyl,
1980;Fig.1).
The Peten Lowland is composed of horizontally-bedded Mesozoic and
Tertiary sediments. Karst topography Is developed on the Cretaceous
carbonates and appears in the upper left corner of the Seasat mosaic (Fig.2a).
The Central American Cordillera is characterized by many Individual
subparal lel ranges mainly oriented east-west. The basement of the range is
composed of metamorphic rocks surrounded by peridotites and serpentinites. To
the north, the sedimentary cover extends from Permo-Carboniferous to
Plio-Pleistocene. Running from Amatique Bay, large faults trend parallel to
the Cordillera. They are (Muehlberger and Ritchie, 1975): the
Cuilco-Chixoy-Polochic Fault (CCP), the Motagua Fault (MO) and the
Jocotan-Chamelecon Fault (JC), (Fig.1 and 3). This zone represents the
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