NEOTECTONIC EVOLUTION OF THE ISTHMUS OF TEHUANTEPEC (SOUTHEASTERN MEXICO)

The Isthmus of Tehuantepec of southeastern Mexico is located near the triple junction of the North American, Cocos and Caribbean plates. A n eotectonic study, including fault tectonic analysis and study of sub-s urface data, was performed in order to understand the tectonic evoluti on of this complex zone. The Plio-Quaternary fault pattern is describe d and the brittle structures are interpreted in terms of palaeostress orientations. We propose a model of tectonic evolution of the Isthmus of Tehuantepec since the Late Miocene (similar to 6 Ma) characterized by extensional tectonics. The present structure of the isthmus results from the superimposition of three distinct types of tectonism: (1) a tilting of the eastern Isthmus during the Late Miocene-Early Pliocene, along a major N-S-trending normal fault zone (the Isthmus Fault Zone) , as a consequence of the deformation of the subducting slab of the Co cos plate along the subducted part of the Tehuantepec Fracture Zone; ( 2) the, subsidence of the southern isthmus in relation to N-S extensio n, associated with the eastward displacement of the western Caribbean plate with respect to the southern North-American plate along the Polo chic-Motagua fault system; and (3) extensions that develop in the nort hern half of the Isthmus related to the evolution of the passive margi n of the Gulf of Mexico. (C) 1998 Elsevier Science B.V. All rights res erved.