Subduction of the Cocos plate in the Mid America Trench.

The Mid America Trench, off the Pacific coast of southern Mexico and central America, is the site of northeastward subduction of the Cocos oceanic plate under the North America and Caribbean plates ¹ (Fig. 1). In Guatemala, the North America and Caribbean plates are separated by the Polochic-Motagua left-lateral strike-slip faults (Fig. 1). The trench itself appears to be divided into two distinct sections at its intersection with the Tehuantepec Ridge. To the south the margin of the trench is wide and consists of a well developed shelf basin ² bounded on the east by a huge volcanic cordillera parallel with the trench axis at a distance of ∼200 km. In contrast, to the north, the margin is narrow and devoid of shelf basin; landwards, the trans-Mexican volcanic belt trends oblique to the trench. This volcanic chain would be anomalous if it were related to the subduction of the Cocos plate off southern Mexico. In 1979, as part of the International Phase of Ocean Drilling (IPOD) of the Deep Sea Drilling Project, Legs 66 and 67 respectively explored the northern (off Acapulco, Mexico) and southern (off San Jose, Guatemala) section of the Mid America Trench ^3-6 (Fig. 1). Since then short topographical surveys of the trench have been carried out by RV Jean Charcot ⁸ using the sea-beam technique ⁷ . We report here that both sets of data, together with UTMSI multichannel seismic profiles ^10,11 can be used to reconstruct the processes of subduction along the Mid America Trench.