Page 191 - Caldera Volcanism Analysis, Modelling and Response
P. 191
166 Gerardo J. Aguirre-Dı ´az et al.
Figure 14 El Ocote ignimbrite at several localities. (a) Out-£ow, near-vent facies of El Ocote
ignimbrite at the Sierra El Laurel, close to the type locality.The ignimbrite is high-grade and
forms well-developed columnar joints.Thickness at this site is 70--120 m. (b) Intra-graben cal-
dera ignimbrite ¢ll of El Ocote ignimbrite, near the fault scarp of Sierra El Laurel.The ignim-
brite is about 400 m thick with no base exposed, and includes co-ignimbrite lithic-lag breccias
(not visible in photograph). (c) Lava-like, rheomorphic fold in extremely high-grade El Ocote
ignimbrite at intra-graben caldera outcrop. (d) Sheath fold (eye-structure) in lava-like, extre-
mely rheomorpic high-grade facies of El Ocote ignimbrite in intra-graben caldera outcrop.
(e) Flat-lying, lava-like, high-grade El Ocote ignimbrite at near-vent out-£ow facies close to
El Ocote. (f) Flat-lying, high-grade El Ocote ignimbrite at the northern out-£ow facies that
formed the Mesa San Jose ¤ de Gracia (MSJG in Figure13a). Pumice is collapsed but not as extre-
mely elongated as in near-vent facies (Figure14e).
