Continental extension tectonics in the Gulf Extensional Province, northern Baja California, Mexico: evidence from low-temperature thermochronology

Abstract

Low-temperature thermochronology on apatites from the Gulf Extensional Province in northern Baja California reveals fission-track ages >27 Ma in the Sierra San Pedro Martír and the Sierra Juarez. This indicates that exposed crustal depths are less than about 2km below the pre-extension land surface. Younger ages are found in the strongly rotated hanging wall blocks in the Sierra San Felipe towards the Gulf coast indicating deeper crustal levels. The more sensitive apatite (U-Th)/He system, however, reveals much younger ages along the foot of the main escarpment and in the San Felipe blocks constraining the time of onset of rapid extension to between 7 and 14 Ma.