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

智力优势：巨大的火山爆发对人类来说是罕见但潜在的灾难性危害，但我们对此类现象的了解相对不完整。一些最年轻的大规模喷发发生在长白山火山（也称为白头山，天池火山），横跨中国/朝鲜边境。 那里的活动与俄勒冈州7.7 ka的火山爆发非常相似？S山马扎马，并形成火山口湖。长白山1 ka大喷发喷发出约100 km 3的过碱性流纹岩（comendites）。这次火山爆发将长白山火山锥冲垮，形成了一个直径超过5公里的破火山口。一个主要的前破火山口喷发的comendites发生在4 ka，和较小的postcaldera喷发的comendites和粗面岩发生在0.3 ka。对1 ka大喷发的辉长岩的初步研究得出锆石结晶年龄为9±1 ka（等时线年龄），比大喷发早约8,000年。本研究的主要目的是了解长白山地区大规模岩浆活动的发生、演化及其锆石年龄的意义。 建议对上述火山喷发产物中的副矿物（锆石和蛇绿岩）进行全面的离子探针238 U-230 Th定年。年轻粗面岩中的锆石晶体也将用U-Th法测年。还将确定锆石、全岩和选定的主要矿物的补充同位素和化学成分。这些数据将[1]允许评价副矿物的形成方式（例如，通过喷发岩浆的直接结晶或通过较老岩浆组分的再循环），以及[2]岩浆在下伏地壳中停留时间的年龄限制。高质量的年代学和地球化学数据的年轻的大体积的长白山过碱性流纹岩也是可取的，因为这种喷发在地球上很少发生。 PI之前已经收集了大量适合分离副矿物的样品，并拥有丰富的离子探针经验和使用UCLS仪器的必要途径;这些因素应该使该项目成为一个高效的项目。更广泛的影响：该项目将加强正在进行的国际合作。它为一名女硕士研究生和两名本科生在EPSCOR州的一个机构提供研究培训。从这个项目中得到的样品将被整合到奥本大学PI教授的火成岩和变质岩石学讲座和实验室中。结果和数据将在高质量的国际期刊上发表，并在国家会议上介绍。这项研究将有助于了解大量人口附近可能发生的灾难性火山爆发。

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.