Structural and petrologic insights into the emplacement of effusive silicic lavas: Inyo Domes, California

Abstract

The Long Valley volcanic region, eastern California, USA is most famous for the caldera-forming eruption which produced the Bishop Tuff ~760,000 years ago. Over the last 3,000 years volcanism has been focused in the western margin of the region through punctuated eruptions of silicic lavas and domes. Three simultaneous effusive silicic eruptions, ~600 years ago, generated three lava domes: Obsidian Dome; Glass Creek Dome; and Deadman Dome which erupted onto vastly different topographies. These domes are exceptionally unique as they erupted variable amounts of two textural and chemical endmember lavas (crystal-rich and crystal-poor) that intimately mixed. The overarching goal of this dissertation is to investigate the magmatic genesis and emplacement styles of these young effusive silicic lava domes. The first chapter of this dissertation investigates the petrogenesis of the three 600-year-old Inyo Domes, concluding they originated from variable mixing of several long-lived, complex, contiguous, magmatic plumbing systems. The second chapter characterizes brittle and brittle-ductile structures preserved across the upper surface of Obsidian Dome, challenging the long-standing theory that the upper surface of silicic lavas is dominated by ductile folding. The third chapter utilizes morphologies classified from analog modeling to characterize the upper surface of Obsidian Dome and Glass Creek Dome to assess the control of underlying topography and crystallinity on lava emplacement rates. The first chapter of this dissertation investigates the petrogenesis of the three 600-year-old Inyo Domes, concluding they originated from variable mixing of several long-lived, complex, contiguous, magmatic plumbing systems. The second chapter characterizes brittle and brittle-ductile structures preserved across the upper surface of Obsidian Dome, challenging the long-standing theory that the upper surface of silicic lavas is dominated by ductile folding. The third chapter utilizes morphologies classified from analog modeling to characterize the upper surface of Obsidian Dome and Glass Creek Dome to assess the control of underlying topography and crystallinity on lava emplacement rates.