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Abstract: Structural Fabric of Serpentinites and Amphibolites along Motagua Fault Zone in El Progreso Quadrangle, Guatemala

Previous HitPaulTop S. Roper

The Motagua fault zone in Guatemala is the landward extension of the Cayman-Bartlett Trough in the Caribbean Sea and represents part of the southern boundary of the North American plate. Large masses of serpentinite have been emplaced along parts of the fault zone during the Late Cretaceous and Tertiary periods. Structural fabric is poorly developed in the serpentinites, though some disharmonic folding is present in these rocks. Near the fault zone the foliation is steeply inclined. Farther north the foliation becomes subhorizontal and is related to massive thrust sheets.

Within and adjacent to the serpentinite are extensive outcrops of a tremolite amphibolite formation. The origin of the amphibolite is complex, but it is due in part to metamorphism of basic igneous rocks and partial metasomatism of preexisting Chuacus metamorphic rocks. Foliation is well developed in the amphibolites, and indicates that most of this formation has experienced at least two phases of folding. The structural fabric in the amphibolites has a distinctly different pattern and orientation from that found in the Paleozoic Chuacus Group indicating that it has a different tectonic origin. The structural fabric in the amphibolites suggests that these features are related to the mode and direction of serpentite emplacement through and over surrounding country rock.

AAPG Search and Discovery Article #90965©1978 GCAGS and GC Section SEPM, New Orleans, Louisiana