EAR-PF: Timescales and processes of magmatic resurgence at Toba caldera

Cisneros, Alejandro Omar, Martinez CA

Investigators

Abstract

Volcanoes like Toba and Yellowstone calderas are the sites of the greatest natural catastrophes produced by the Earth: supereruptions. It is no surprise then that significant effort has been put into understanding the nature of these eruptions, their hazards, and the risk they pose to society. However, whereas the build-up to supereruption is now well understood, what happens after a supereruption, the recovery period known as resurgence, is still poorly understood. This is important because all active supervolcanoes on Earth are in this state and still pose a significant hazard. This project seeks to fill this knowledge gap and improve our ability to assess future hazards and risks at supervolcanoes by studying the events after the largest supereruption in the last 2 million years: the Youngest Toba Tuff (YTT; ca. 74,000 years BP) from the Toba Caldera in Indonesia. As an NSF EAR Postdoctoral Fellow, Dr. Cisneros de León will integrate time, chemistry, and temperature information recorded in microscopic crystals erupted at Toba to build a history of the physical and chemical conditions in the magma during recovery after the supereruption. This approach will also reveal the history of eruptions since the supereruption, and allow estimation of the volume of eruptible magma present today beneath the Toba supervolcano enabling better assessment of future risk. The goal of this proposal is to use Toba caldera as a natural laboratory to resolve time and spatial scales of the magmatic processes governing post-caldera resurgence at supervolcanoes. This will be achieved by integrating petrochronology, thermochronology, diffusion, and thermochemical modeling using zircon, allanite, monazite, apatite, sanidine, and quartz to decipher the complementary records of these crystal phases as they pertain to the post-caldera plumbing system and its compositional evolution over decadal to millennial timescales. The specific aims are to 1) develop an integrated petrogenetic approach for investigating pre-eruptive silicic magma reservoirs at all scales based on time, temperature, and chemistry recorded in multiple accessory and major mineral phases; 2) use this information to infer the physicochemical state of pre-eruptive magma storage; and 3) determine the rates at which magmatic processes promote post-caldera eruptions. To accomplish these goals, this study will apply noble-gas 40Ar/39Ar and (U-Th)/He thermochronology to exploit differing closure temperatures of Ar- in sanidine and He- in zircon, monazite, and apatite to resolve eruption ages, storage conditions, and extrusion rates of effusive volcanism from selected post-caldera eruptions. In addition, high-spatial-resolution secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) will be employed on accessory mineral phases and quartz to determine absolute and relative timescales, respectively, paired to elemental and isotopic compositions. Finally, data from various crystal-scale records will be integrated into thermochemical models to evaluate the current state of the magma system at Toba and the driving forces for resurgent uplift. Thus, constraining the timescales, conditions, and extent over which magmatic processes are occurring in resurgent reservoirs will make a fundamental contribution to eruption forecasting, especially when geophysical approaches are challenged to characterize melt-containing reservoirs at high resolution. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.