Page 180 - Caldera Volcanism Analysis, Modelling and Response

The Sierra Madre Occidental, Mexico 155

Figure 4 Index map of Basin and Range grabens in the southern sector of the SMO; (a) regio-
nal location of the southern sector in Mexico and of Figure 5b. Location and names of the gra-
ben at the southern SMO, and of other regional structures, such as the Gulf-coast extensional
province and of theTepic-Zacoalco graben. Stars indicate sites of ¢ssure type vents. Lines indi-
cate major normal faults (with permission from Google).

In these two volcanic fields there are examples of graben calderas and fissure vents
that were controlled by the regional extension of Basin and Range tectonics
(Trista ´n-Gonza ´lez et al., 2006), and both include the widespread volcanic unit
called Panalillo Inferior ignimbrite, whose feeder vents are related to pyroclastic