Histories of Large Silicic Magma Evolution at Changbaishan Volcano: Insights From Accessory Minerals

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Intellectual Merits: Huge explosive volcanic eruptions represent rare but potentially calamitous hazards to mankind, yet our understanding of such phenomena is relatively incomplete. Some of the youngest large-scale eruptions occurred at the Changbaishan volcano (also named Baitoushan, Tianchi volcano) that straddles the border of China/North Korea. Activity there closely resembles the 7.7 ka climactic eruption of Oregon?s Mt. Mazama, and formed Crater Lake. The great 1 ka Changbaishan eruption erupted ~100 km3 of peralkaline rhyolites (comendites). This eruption decapitated the Changbaishan volcano cone, forming a caldera over 5 km across. A major pre-caldera eruption of comendites took place in 4 ka, and smaller postcaldera eruptions of comendites and trachytes took place at 0.3 ka. Preliminary studies of comendites from the 1 ka eruption yield a zircon crystallization age of 9±1 ka (isochron age), that predates the great eruption by about 8,000 years. The main objective of this proposal is to understand generation and evolution of large volume silicic magmatism at Changbaishan and the significance of these older zircon ages. It is proposed to conduct comprehensive ion microprobe 238U-230Th dating of accessory minerals (both zircons and chevkinites) in comendites from the aforementioned eruptions. Zircon crystals from young trachytes will also be dated by the U-Th method. Complementary isotopic and chemical compositions of zircons, whole rocks and selected major minerals will also be determined. These data will [1] allow evaluation of the mode of formation of accessory minerals (e.g., by direct crystalliztion of the erupted magmas or by recycling of older magmatic components), and [2] age constraints for magma residence times in the underlying crust. High-quality geochronological and geochemical data on the young large volume Changbaishan peralkaline rhyolites is also desirable, owing to the rare occurrence of such eruptions on Earth. The PI has previously collected large samples suitable for separations of accessory minerals, and has extensive ion microprobe experience and the necessary access to the UCLS instrument; these factors should make this a highly efficient project.Broader impacts: The project will enhance ongoing international collaboration. It provides research training for a female Master graduate student and two undergraduate students at an institution in an EPSCOR state. Samples resulting from this project will be integrated in Igneous and Metamorphic Petrology lecture and lab taught by the PI at Auburn University. Results and data will be published in quality international journals and presented at national meetings. The study will contribute useful knowledge of potentially catastrophic eruptions near large populations.