Abstract
Flows, dikes, and remnant constructional features of ultramafic inclusion-bearing alkaline basalts, well known from the central Mojave, are also present near its southern boundary with the San Andreas fault at Fry and Ruby Mountains. Ultramafic inclusions from these localities are predominantly spinel lherzolites and harzburgites. A single, 200-gram garnet websterite inclusion found at Fry Mountain is only the second one reported in alkaline basalt from the western United States. All ultramafic inclusions from these localities exhibit tectonic textures and are believed to be accidental fragments of upper mantle material incorporated into basanite melts at temperatures between 950 and 1200°C and pressures between 9 and 23 kbar. Inclusion-bearing basaltic volcanism in the Fry and Ruby Mountain areas occurred between 6 and 10 million years ago, whereas comparable volcanism in the central Mojave beyond the transpressional tectonism of the San Andreas fault has continued into the Quaternary.
