EAR-0125779 Busby and Gans University of California, Santa Barbara
This Collaborative Research proposal between the UC Santa Barbara and the University of Southern Mississippi will establish a regional stratigraphic structural and geochronological framework for Miocene volcanic rocks of the northern to central Sierra Nevada, and at the same time reconstruct structural settings and volcanological processes. The main motivation is to evaluate the tectonic significance and relationship of these mid-Miocene volcanic rocks to modern and ancient subduction, Basin and Range extension, and hotspot settings. Detailed volcanic and sedimentary lithofacies maps will be produced and used to determine the nature and timing of synvolcanic faulting. Petrography, image analysis and Scanning Electron Microscope (SEM) imaging of the Sierran breccias will be employed to study and quantify clast and matrix types, morphologies, dimensions and fragmentation styles (brittle, ductile, transitional), and results will be compared with published examples of volcanic breccias of all plausible origins. Preliminary XRF geochemical analysis of representative suites (including all samples to be dated) will be completed and compared with compositions of clasts with matrices in the breccias. To test for geological consistency in our age data, sampling for 40Ar/39Ar geochronology will concentrate on stratigraphic successions containing at least three or four different datable units. Ar geochronology of single mineral grains (total fusions) as well as incremental step heating experiments will be completed.
