Reassessment of the Paleogene position of the Chortis block relative to southern Mexico: hierarchical ranking of data and features
Morn-Zenteno, D.J.*, Keppie, J.D., Martiny, B., Gonzlez-Torres, E.Instituto de Geologa, Universidad Nacional Autnoma de Mxico, Ciudad Universitaria, Delegacin Coyoacn, C.P. 04510 Mxico D.F., Mxico
The Paleogene location ofthe 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 Cenozoicreconstructions: (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 presentposition, 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 andrelevance: 1st order plate tectonic features that define the relative motion and amount of displacement of the plates, paleomagnetic data that provide paleolatitudinal constraints, and essential elementsfor any model; 2nd 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; and3rd 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 NorthAmerica 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 uncertaintiesin 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...
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