9706682 Hausback This project aims at studying the poorly known Sutter Buttes, an isolated volcano that contain the only indigenous mag matic rock exposures in the entire Central Valley of California. The volcano is composed of a central core of volcanic domes surrounded by a large fragmental apron that record a lengthy evolution of explosive volcanism in this area. The volcanic rocks of Sutter Buttes represent a diverse sub-alkalic suite ranging from rhyolite to mafic andesite that erupted in early Pleistocene time, during the profound tectonic transition from subduction to transform faulting, of the western North America plate boundary. This unique tectonic setting of the Sutter Buttes provides an unprecedent opportunity to understand magma production during this type of transition. It is proposed to establish a framework of integrated geological mapping, petrographic documentation, microprobe mineral analyses, and 40Ar/39Ar geochronologic studies of the volcanic rocks and their basement. At this stage, it is unclear if the Sutter Buttes are related to any other magmatic feature, such as the Cascades or to the young volcanic activity in the Sonoma and Clear Lakes areas. The results of this work should constrain some of the genetic features of this unique volcano and help put its magmatism into the regional tectonic framework.
