ON THE INFLUENCE OF BASEMENT STRUCTURES ON THE LOCATION OF SOME INTRAPLATE-TYPE VOLCANIC FIELDS IN CENTRAL AND NORTHERN MEXICO

A large number of late Cenozoic mafic alkalic volcanic fields occur in northern and central Mexico. Often, these volcanic rocks contain upper mantle xenoliths, and/or complex sets of accidental megacrysts, and/or feldspathic granulite inclusions from deep portions of the continental crust. Even tough most volcanic fields appear to be randomly distributed in the southern portion of the Basin and Range or in Gulf of California Extensional Province, the presence of xenolith-bearing alkalic volcanic rocks in places like San Quintín (Baja California) and Llera de Canales on the Gulf of Mexico coastal plain indicates that the intraplate-type magmatism is independent of present-day geologic or tectonic provinces. Most volcanic fields are small volume and composed by few isolated scoria cones and associated lava flows. Notable exceptions are the Pinacate (416 vents), Camargo (>300), and Durango (>100) volcanic fields, where lavas cover areas of 1500, 3000, and 2100 km², respectively. Lutz and Gutmann (JGR, 100, 1995) showed that the Pinacate location and vent distribution within the field are influenced by B&R horizontal stress regime and a N55W-trending major regional fracture zone. Camargo lays atop a buried portion of the N60W-trending San Marcos Fault, at its intersection with the Bolsón de Mapimí, a major B&R, N-S structure. We have documented evidence that San Marcos, a major fault formed during the Jurassic, was reactivated at least twice during the late Cenozoic, including at the time of volcanism in Camargo. The Durango v.f. is at the intersection between the N55W-trending San Luis-Tepehuanes fault system with the northern extension of La Ventana Graben, which in its southern portion merges with a large set of normal faults in the Gulf of California Extensional Province and farther north is undistinguishable from B&R faults exposed east of Durango City. Additional examples of the control exerted by N50-60W-trending faults can be found at Las Esperanzas v.f. (Coahuila) located near La Babia fault, and in the Santo Domingo and Los Encinos v.f. lay lay on the San Tiburcio lineament. Likewise, the vents of Ventura-Espírtu Santo are located as small isolated clusters along the influence zone of the San Luis-Tepehuanes fault system. Evidence of one or more reactivations of the NW-trending systems may be found in several places.