EXTENSIONAL TECTONICS OF CENTRAL-NORTHERN MEXICO

The Baja California Peninsula separation resulted from tectonic processes related to extensional activity in central-northern Mexico, which formed the Mid-Gulf of California Rise (MGCR). This oceanic rift system and adjacent extension in continental regions, dominated the Neogene-Quaternary structural behavior in the central-northern part of Mexico.

Normal faults of NW-SE strike are the dominant structure of the Sonoran Desert, Sierra Madre Occidental, Basin and Range, Central Plateau and Sierra Madre Oriental physiographic provinces. In this region of the North American Plate, continental crust displacements are related with tilted block faults bounded by steep dipping normal faults. Despite most blocks-fault are tilted from the northeastern to the eastern direction, there exist a few crustal blocks with opposing- and no-tilting direction.

Numerous hot springs, Neogene cinder volcanic structures and northwest trending Holocene open-fissures developed on alluvial valleys, are all associated with normal block-faults. Most of the seismic activity at the northern part of the Transmexican Volcanic Belt is concentrated along the MGCR. However, earthquake epicenters on contiguous continental regions of the mentioned physiographic provinces are directly related to normal fault extension. Seismicity is continuously recorded by a seismometer-station net, recently installed.

Seismicity, together with structural, geomorphic and paleomagnetic evidences, indicate that most of the northern Mexican physiographic provinces are currently experiencing distension. This work belongs to the research project 167638, granted by SEP-CONACYT from Mexico.