Normal faulting in the Pathé geothermal area, Central Mexico

Abstract

The Pathé geothermal area is located in Late Miocene to Pliocene volcanic rocks in a region of active normal faulting. These faults cluster in sets striking near E-W and close to N-S. The east-west fault set is the southern extension of the Aljibes half-graben whose master fault is curved and has a composite vertical offset of 480 m. Near-surface vertical displacement is up to 70 m, while E-W faulting is generally located along a 34 km long semielliptic area of plateau basalts and cinder cones. The N-S faulting defines the San Francisco graben, with vertical offsets of around 30 m, increasing up to 180 m below the surface. Neogene rocks are intruded by numerous roughly east-west trending dikes and northsouth trending stocks. Steam production occurs at the intersection of the eastern San Francisco graben with east-west faulting. Hot spring activity is located on an E-W trending fault. Hydrothermal alterations along fault and fracture segments suggest earlier geothermal activity.