Development of a Micro-baddeleyite (ZrO2) U-series Chronometer for Recent Mafic Lavas

重建过去火山爆发前后的年表，对于了解人类对自然灾害的反应模式，以及为现有的火山灾害制定缓解战略至关重要。尽管许多用于第四纪火山喷发年代测定的地质年代学技术已经成熟，但在岩浆过程最终剧烈喷发的时间，以及它们对环境的影响，甚至对最近发生的事件的影响方面，仍然存在相当大的不确定性。这项研究将为常见类型的火山开发一种测年工具，其特征是相对较低的硅丰度，这很难用现有的计时器进行测年。最终，对这类火山喷发历史的年龄限制的改进将有助于更好地评估其火山危险性。这种新的计时器是基于氧化锆矿物baddeleyite晶体中固有的铀的放射性衰变。坏辉石的晶体尺寸通常很小，因此本研究将改进电子束技术，用于定位岩石中的微坏辉石晶体，并开发分析方法，通过二次电离质谱分析坏辉石，以检测痕量铀及其放射性衰变产物的丰度。将对具有代表性的火山进行调查，以使巴德雷特天文钟与其他测年技术相比较。为此，加州大学洛杉矶分校的研究人员正在与国内外火山学家合作。案例研究包括喀斯喀特山脉（美国）和坎帕尼亚火山省（意大利）的火山。这些火山代表了长期存在的火山系统，具有长达数万年至数十万年的周期性喷发历史。通过坏辉岩铀不平衡定年建立精确的火山年代地层学，最终将有助于提高对广泛岩浆环境下岩浆输出速率和喷发复发间隔的理解。

Reconstructing the pre- and post-eruptive chronology of past volcanic eruptions is essential for understanding the patterns of human response to natural disasters, and to devise mitigation strategies for extant volcanic hazards. Despite the maturity of many geochronological techniques applied to date Quaternary volcanic eruptions, considerable uncertainties remain with regard to the timing of magmatic processes culminating in violent eruptions, as well as their environmental impact even for fairly recent events. This research will develop a dating tool for common types of volcanoes characterized by comparatively low silica abundances, which can be difficult to date using existing chronometers. Ultimately, improved age constraints on the eruptive history of such volcanoes will lead to better assessments of their volcanic hazards.The new chronometer is based on the radioactive decay of uranium intrinsic to the crystal lattice of baddeleyite, a zirconium oxide mineral. Crystal sizes for baddeleyite are typically small, and therefore this research will improve electron-beam techniques for locating micro-baddeleyite crystals in rocks, and develop analytical procedures to analyze baddeleyite via secondary ionization mass spectrometry to detect trace abundances of uranium and its radioactive decay products. Representative volcanoes will be investigated to calibrate the baddeleyite chronometer against other dating techniques. For this, University of California Los Angeles researchers are collaborating with domestic and international volcanologists. Case studies include volcanoes in the Cascades (USA) and the Campanian volcanic province (Italy). These volcanoes represent long-lived volcanic systems with a protracted history of recurrent eruptions over tens to hundred thousands of years. Establishing precise and accurate volcanic chronostratigraphies through baddeleyite uranium disequilibrium dating will ultimately contribute to an improved understanding of magma output rates and eruptive recurrence intervals in a broad range of magmatic environments.