The following message is being shared on behalf of Semira Alekic and the Department of Earth Sciences.
The Department of Earth Sciences welcomes you to their Seminar Series featuring:
Dr. Fatema Panahi Postdoctoral Fellow Department of Earth Sciences, University of Manitoba
The three-million-year pulse: pace and processes of Late Jurassic magmatism in the Sierra Nevada arc
March 3, 2026 223 Wallace Building 1:00 PM
Continental arcs commonly experience brief, high-flux magmatic pulses, and the Late Jurassic Sierra Nevada arc records one such event in the form of a bimodal suite of highly silicic plutonic, hypabyssal, and volcanic rocks, associated cumulate gabbros, and a regionally extensive andesitic dike swarm. This study presents new constraints on the timing, magma sources, differentiation, and genetic relationships of this bimodal igneous episode and the andesitic dike system. High-precision CA-ID-TIMS zircon geochronology, whole-rock Sr-Nd-Pb isotopic data, trace-element geochemistry, and zircon δ18O data are integrated to characterize the evolution of this magmatic system. Geochronological data constrain all magmatic activity to a narrow interval (152-149 Ma), indicating that the bimodal suite and andesitic dike swarm are coeval. Geochemical and isotopic data indicate that the andesitic magma served as the parental melt, from which high-silica, crystal-poor volcanic, hypabyssal, and plutonic rocks formed as interstitial melts, whereas the mafic cumulate gabbros represent the residuum. Geochemical patterns, including mantle-like zircon δ18O values, evolved Sr, Nd, Pb isotopic signatures, and trace-element systematics, point to partial melting of the hydrated lower crust or subcontinental lithosphere to generate the parental andesitic magma, which then differentiated in shallow, deformation-influenced reservoirs to generate the bimodal suite.