Sediment fill in the Middle America Trench inferred from gravity anomalies

Abstract

A sequence of free-air gravity anomaly profiles across the Middle America Trench are used to model the sediment fill of unconsolidated pelagic and hemipelagic sediment facies, and partially altered bedrock material. The shift of the free-air forearc low from the bathymetric minimum in the trench is used to estimate the amount of low-density sediment. The gravity effect of the fill is relatively small, suggesting that the dominant processes in the Middle America trench are sediment subduction and scraping of unconsolidated pelagic sediments from the top of the subducting oceanic plate. The sediment volume in the trench tends to increase southward from Jalisco to Oaxaca. In the Guatemala basin this tendency is less clear. There is some correlation between the amount of fresh sediment fill and the convergence rate at the trench, except for the profiles with an extensive terrigenous sediment contribution or the areas of subduction of prominent bathymetric features.