Range front faulting and volcanism in the Mono Basin, eastern California

The spatial and temporal pattern of range front normal faulting and volcanism in the Mono Basin of eastern California suggests that dikes are being intruded underneath the Mono Craters in response to crustal stretching and are now accommodating strain that was once taken up by range front faulting. The section of the Sierra Nevadan range front near the craters accommodated as much as 1 mm/yr of extension as recently as about 40 000 years ago. For the past 40 000 years, this section of range front has been inactive, even though range front extension to the north and south has continued at up to 0.9 mm/yr. For the past 40 000 years, dikes, intruding underneath the Mono Craters, seem to have been accommodating the 1 mm/yr of extension that was previously taken up by faulting. Since the basin is extending obliquely to the trend of the frontal faults, there is a component of dextral shear to their motion, so that the Mono Craters may be forming on an extensional boundary of a pull-apart basin. If the craters represent incipient caldera formation, then calderas such as Long Valley may also have formed in pull-apart zones. -Authors