NEOTECTONICS IN CENTRAL MEXICO

Regional neotectonic activity in central Mexico was mapped through analysis of eleven Landsat Thermatic Mapper images. The study area stretches from Mexico City on the east to the Gulf of California on the west, between 17-degrees and 21-degrees-N latitude. Fault scarps of Plio-Quaternary age define several large scale tectonic features within the Mexican Volcanic Belt, dominated by rifting, transtension, and shear, with probable sinistral components. Three large crustal blocks south of the Mexican Volcanic Belt are separated from the North American Belt are separated from the North American plate and from each other by zones of neotectonic activity that express the relative motions between the adjacent blocks. A simple vector diagram for plates and crustal blocks in central Mexico has been constructed using information from the literature combined with the orientation of fault zones as mapped in this study. The relative motion between the blocks varies from about 2.5 to 8 mm year -1, which is comparable to motions of crustal blocks in area of active rifting in other parts of the world. In the Mexican Volcanic Belt, there is a clear relationship between volcanism and neotectonic activity. Fault zones that traverse nearly the entire region have the same location and orientation as the volcanic belt. This may indicate that deformation within the crust of the overriding slab plays a significant role in determining the unusual orientation of the Mexican Volcanic Belt relative to the trench. The ultimate factor controlling the location of Plio-Quaternary volcanism and tectonism in central Mexico may be large zones of crustal weakness formed during major Mesozoic and Cenozoic tectonic events.