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Geophysics Department Seminar - "Restless magma and rapid uplift: Active fault control of a large silicic magma chamber" - Dr. Katie Keranen, Cornell University
Restless magma and rapid uplift: Active fault control of a large silicic magma chamber
Explosive eruptions of large rhyolitic systems are common in the geologic record and pose a major threat to society. One large rhyolitic system, the ~50 km2 volcanic field at Laguna del Maule (LdM), Chile, is uplifting at the nearly unprecedented rate of 20-25 cm/year since 2007 with no modern eruptions. The volcanic field contains the highest volume of post-glacial high-silica rhyolites in the Andes, with flows as young as 2 ka encircling a ~50-m deep lake dammed by one of the volcanic flows. Here we show results from a seismic survey on the lake, using a 3.5 kHz CHIRP system to image sediments to depths of ~10 meters. The seismic imaging, earthquake locations, focal mechanisms, and onshore fault mapping indicate that 1) the magma chamber formed beneath an extensional pull-apart basin; 2) this Holocene basin is now inverted and actively uplifting with a central dome beneath the lake, 3) faults sharply cut lake sediments to the lake floor, indicating continued, active faulting directly above the region of greatest uplift, and 4) magmatic dikes rise to the lake floor along the fault traces. These large rhyolitic chambers, with residence times of hundreds of thousands of years, may be triggered by rapid magmatic recharge (Jellinek and DePaolo, 2003). Results from LdM indicate that the fault system controls and facilitates magmatic processes, though further work is required to determine whether the presence of the active faults increases or decreases explosive hazard.