Tectonics of the Middle America trench offshore Guatemala

ABSTRACT

A geophysical and geological survey conducted over the landward slope of the Middle America Trench offshore Guatemala has revealed lanward - dipping reflectors which are associated with high compressional wave velocities, large magnetic anomalies, and basic/ultrabasic rock. Multifold seismic reflection data reveal that the edge of the continental shelf is a structural high on which Cretaceous and younger sediments of the shelf basin onlap and pinch out. The upper part of the continental slope is covered in most places by a 0.5 to 1.0 km thick sediment apron with seismic velocities of 1.8 to 2.6 km/sec. Immediately beneath the sediment apron an irregular surface is the top of an interval with velocities of 4.3 to 4.7 km/sec. Within this interval landward - dipping reflections are traced to about 6 km below sea level. Above this zone of dipping reflectors two positive magnetic anomalies are observed as well as a positive gree - air gravity anomaly reported by other workers (AU)