SEDIMENT FILL OF THE MIDDLE AMERICA TRENCH INFERRED FROM GRAVITY

Free-air gravity anomalies have been used to examine the sediment fill in the Middle America Trench (MAT), where pelagic and hemipelagic sediments and partially altered bedrock material can be found. A difference between the locations of the observed free-air gravity fore arc low and the bathymetric minimum (trench) is used to estimate the sediment thickness. The gravity effect of the trench sediments is relatively small and suggests that the dominant process along the MAT is sediment subduction. The amount of sediment fill increases from Jalisco (NW end of the MAT) to Oaxaca (SE end of the MAT) while farther to the SE, in the Guatemala basin trench, the sediment fill is practically constant. A correlation between the oceanic plate age at the trench and the amount of sediments exists but this correlation is affected by the terrigenous sediment contribution. In the south-eastern part of the MAT (Guatemala Basin) this type of correlation cannot be established because of the poor knowledge of the plate age distribution along the trench.