Abstract

MORAN-ZENTENO, Dante J.; KEPPIE, Duncan J.; MARTINY, Barbara  and  GONZALEZ-TORRES, Enrique. Reassessment of the Paleogene position of the Chortis block relative to southern Mexico: hierarchical ranking of data and features. Rev. mex. cienc. geol [online]. 2009, vol.26, n.1, pp.177-188. ISSN 2007-2902.

The Paleogene location of the Chortis block relative to southern Mexico is presently a hotly debated topic, with various types and qualities of data brought to bear on the topic. There are currently three competing Cenozoic reconstructions: (i) the traditional model that places the Chortis block adjacent to southern Mexico, (ii) the near in situ model in which the Chortis block is located relatively near to its present position, and (iii) the Pacific model that places the Chortis block WSW of its present location. To provide some order to this debate, we rank data into three levels on the basis of reliability and relevance: 1^st order plate tectonic features that define the relative motion and amount of displacement of the plates, paleomagnetic data that provide paleolatitudinal constraints, and essential elements for any model; 2^nd order piercing points that can be matched in both continental areas, the Chortis block and southern Mexico, and Cenozoic magmatic arcs that can predict plate tectonic scenarios; and 3^rd order pre-Cenozoic features. The orientation, size and patterns of the magnetic anomalies in the Cayman Trough have been interpreted in terms of 1100 km of relative sinistral motion between North America and the Caribbean since 49 Ma and favor the Pacific provenance of the Chortis block from a WSW position, however, internal deformation of the Chortis and Maya blocks as well as uncertainties in the identification of old segments of magnetic anomalies suggest that the relative displacement between the Chortis and Maya blocks could be at least 200 km less. The traditional model, although satisfying two 1^st order criteria, contravenes another 1^st order element, namely the undeformed nature of the Cenozoic sediments in the Gulf of Tehuantepec, which requires a re-evaluation of the model. The interpretation of a Paleogene intra-Pacific position for the Chortis block, southwest of its present position, is more compatible with first order data and resolves some incompatibilities of the traditional model but its viability largely depends on the revision of the total Cenozoic Caribbean plate displacement relative to North America and the Cretaceous trajectory of the Chortis block.

Keywords : tectonics; paleogeography; Chortis block; Caribbean plate; southern Mexico.

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