Late Miocene to Quaternary extension at the northern boundary of the Jalisco Block, western Mexico: The Tepic-Zacoalco Rift revised

Abstract

In the last decade several tectonic models have considered the Jalisco block (JB) as an incipient microplate which is rifting away from mainland Mexico since Pliocene time due to an eastward “jump” of the East Pacific Rise. These models predict normal and right-lateral faulting along the northern boundary of the JB, called the TepicZacoalco rift (TZR). However, the Plio-Quaternary kinematics of the Jalisco block has remained unclear due to the scarcity of structural data along its boundaries. We present a new picture of the structure, the kinematics and time of deformation along the TZR obtained by geological and structural mapping integrated with subsurface stratigraphic data provided by deep geothermal drilling. What has previously been defined as the TZR is actually a combination of different fault systems developed during Late Miocene (12‐9 Ma), Early Pliocene (5.5‐3.5 Ma) and, to a lesser extent, in Late Pliocene to Quaternary times. These structures can be grouped in three branches: 1) a northwestern branch, named the Pochotitan fault system, consisting of listric faults belonging to the Gulf Extensional Province; 2) a central branch made of en echelon grabens which reactivated the boundary between the JB and the Sierra Madre Occidental; 3) a southern branch constituted by detachment faults located inside the Jalisco block. The Pochotitan fault system is composed of northnorthwest‐trending, high angle normal faults which tilt up to 35° towards east-northeast blocks of the Sierra Madre Occidental succession. These faults accommodate at least 2,000 m of vertical displacement related to 12‐9 Ma “Protogulf” extension. The central branch consists of two composite grabens developed along an older transcurrent deformation zone. The western one, the Compostela-Ceboruco graben, is a complex asymmetrical depression developed during Late Miocene and Pliocene time with vertical displacement exceeding 2,000 m. Toward the east is the Plan de BarrancasSanta Rosa graben, a west-southwest‐trending and 30-km-wide depression, bounded to the north by the Santa Rosa-Cinco Minas fault and to the south by the Plan de Barrancas fault and its buried southeastern prolongation detected by geophysical studies under the Tequila volcano and the southwestern part of La Primavera caldera. The graben displays a total vertical displacement of ~550 m mainly achieved during early Pliocene time. The southern branch is formed by the Amatlan de Canas half-graben