Paper No. 27-12
Presentation Time: 9:00 AM-1:00 PM
ZIRCON AND TRACE ELEMENT ANALYSIS OF THE INDEPENDENCE DIKE SWARM
Late Jurassic subduction of the Farallon oceanic plate under the western continental margin of North America led to abundant magmatism in the Sierran Arc. This era of arc magmatism is responsible for magmatism throughout Eastern California including the 148 Ma Independence Dike swarm. The Independence Dike swarm spans the Mojave Desert to the Garlock fault, where it is offset and continues through the Alabama Hills, Spangler Hills, and into the Inyo Mountains and eastern Sierra Nevada (Moore and Hopson, 1961; Smith 1962). The Independence Dike swarm remains understudied, particularly the more southern dikes in the Mojave and Stoddard Wells area. More recent research has extended the range of the swarm further south, establishing the swarm’s importance as chronological and structural markers across the Garlock fault and records of the rotations and movements of crustal slivers in the Late Mesozoic and Cenozoic (James, 1989). Though much of the swarm is mafic, the dikes range in composition from high silica rhyolite to andesite to basalt as most mafic and locally are highly alkalic (Carl and Glazner, 2002). This study examines the chemistry of several high silica Independence Dikes from sites in the Mojave Desert and Owens Valley using zircons and trace element analysis. Utilizing samples from a variety of dikes across the swarm, the study is composed of comprehensive outcrop testing how similar or dissimilar Independence Dikes are from one another at local scale. One study area at Stoddard Ridge is shown to have 30% dike area and both crystal poor and crystal rich rhyolites as well as previously unrecognized intermediate dikes. New geochronologies of these test areas are working to understand the segmented emplacement of groupings of dikes. Trace element analysis of another study area has dikes clustering around specific concentrations rather than continuous fractionation trends, suggesting that these dikes follow the multiple phases of emplacement. This study offers insight into the complexities of Late Jurassic magmatism and the Independence Dike swarm’s compositional variety.