Active rifting and crustal thinning along the Rivera-Cocos plate boundary as inferred from Mantle Bouguer gravity anomalies

Abstract

The El Gordo graben lies within the oceanic lithosphere west of the Middle America Trench at 18.15°N, 104.7°W. This graben has been proposed to mark the southwest tip of an active zone of extension located between the Rivera and Cocos plates. The results of an analysis of the Mantle Bouguer gravity anomalies in the area of the El Gordo graben, and in the area located between the graben and the East Pacific Rise, are consistent with this proposal, as well as the proposal that the zone of extension may be propagating towards the East Pacific Rise. Specifically: (1) A prominent decrease in the MBA values occurs in the area of the El Gordo graben, the maximum decrease being centered over the El Gordo volcanic complex, located in the center of the graben. This decrease is modeled as being the result of magma intrusion within the oceanic crust of the graben centered under the El Gordo volcanic complex. This model is supported by high surface heat flow in the area of this complex. (2) A NE-SW free-air gravity high is observed to extend from the El Gordo graben to the East Pacific Rise. However, only the western part of this anomaly is observed in the MBA map. Modeling of the MBA values indicate that this anomaly may be due to crustal thinning in this region. However, unlike the area of the El Gordo graben, gravity and bathymetric data is sparse in this area, so this result should be considered as preliminary.