LOPEZ, ARRIAGA, FERNANDO, Las Brujas, MExico

ABSTRACT: Tertiary Tectonic in the Tehuantepec Isthmus, Mexico

A microplate model in the basement was proposed according to photointerpretation of satellite imagery and supported with microtectonic studies in the Tehuantepec's Isthmus. The microplate is located in the northwestern part of the "Sierra de Chiapas," and structurally has lineaments that correspond with sinestral wrench faults oriented northeast-southwest and dextral faults oriented northwest-southeast. In the front of the microplate, these faults are joined in an arc form.

The microplate began its movement forward to the north in the middle Tertiary. This movement originated in a regional compressional stress that was younger to the north. The stress changed the orientation of the anticline axis from northwest-southeast to west-east. In its western limit, the stress produces a sinestral shear stress that built a rotational deformation in the "Sierra Atravesada," and represents a superimposed tectonic block over an ancient (laramide) orogeny. This system has also produced other secondary transtensional effects oriented northwest-southeast, represented along the "Depression Central del Istmo."

The microplate has formed a tensional system opening the "Superior, Inferior, and Mar Muerto" lagoons. The microplate is strongly related with the relief, seismic activity, and the tectonics of the salt of the Tehuantepec's Isthmus.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.