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Abstract

The Middle Miocene, thin-skinned, Chiapas fold-and-thrust belt (Gulf of Mexico–southeastern Mexico–Belize) consists of WNW-trending folds and thrusts, and East–West sinistral transcurrent faults resulting from N60°E shortening. Balanced cross-sections indicate that shortening varies from 48% (SW) to c. 8% (NE) with a total shortening of 106 km, and that thrusts merge into a basal décollement in the Callovian salt horizon. The Middle Miocene age of the deformation is synchronous with collision of the Tehuantepec Transform/Ridge with the Middle America Trench off Chiapas. The presently exposed Tehuantepec Transform/Ridge varies from a transform fault across which the age of the oceanic crust changes producing a step (down to the east) to a ridge resulting from compression following a change in plate motion and a series of seamounts. On the other hand, the earthquake data show that the part of the Tehuantepec Transform/Ridge subducted during the past 5 Ma is a step with no accompanying ridge. Whereas collision of a ridge segment with the trench is inferred to be responsible for the 13–11 Ma deformation in the upper plate, its termination at 11 Ma suggests an along-strike transition to a step. Collision of the Tehuantepec Transform/Ridge also appears to have terminated arc magmatism along the Pacific coast of Chiapas. The similarity between the petroleum-producing, Cantarell structure in the Sonda de Campeche and the buried foldbelt in the Sierra de Chiapas suggests there is considerable further hydrocarbon potential.

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