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

重建过去火山喷发的喷发前和喷发后的年表，对于了解人类对自然灾害的反应模式和为现有的火山灾害制定减轻战略至关重要。尽管第四纪火山喷发迄今应用的许多地质年代学技术已经成熟，但关于岩浆作用最终导致剧烈喷发的时间及其对环境的影响，即使是最近发生的事件，仍然存在相当大的不确定性。这项研究将开发一种常见类型的火山的测年工具，其特点是二氧化硅丰度相对较低，这可能很难使用现有的计时器进行测年。最终，改善对这类火山喷发历史的年龄限制，将有助于更好地评估它们的火山危害。新的计时器基于斜方铅矿晶格中固有的铀的放射性衰变，斜方铅矿是一种氧化锆矿。斜纹石的晶体尺寸通常较小，因此本研究将改进电子束法在岩石中定位微斜纹石晶体的技术，并开发二次电离质谱仪分析斜纹石的分析方法，以检测铀及其放射性衰变产物的痕量丰度。将对具有代表性的火山进行调查，以根据其他测年技术校准斜晶石计时器。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德(美国)和坎帕尼亚火山省(意大利)的火山。这些火山代表着长寿的火山系统，具有数万到数十万年来反复喷发的漫长历史。通过斜晶石铀不平衡测年建立精确和准确的火山年代地层学，最终将有助于更好地了解广泛岩浆环境中的岩浆产出速率和喷发复发间隔。

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.