U-Series Crystal Ages and Implications for Magma Dynamics

了解火山下岩浆的演化方式以及它们演化的时间尺度，对于了解火山系统如何运作以及提高我们预测火山爆发的能力都很重要。在地表喷发的火山岩中的晶体包含了它们与地表下岩浆相互作用的化学记录，因此这些晶体的年代测定可以提供系统内随时间变化的化学变化信息。然而，不同类型的晶体（例如锆石和斜长石）的年龄通常会产生不同的特征年龄。目前尚不清楚这是由于分析的规模（锆石的单个晶体与斜长石的数千个晶体的集合体相比），还是由于锆石和斜长石通常在不同类型的火山系统中进行分析（大型的火山口形成系统用于锆石，较小的系统用于斜长石），或者因为这两种类型的晶体记录了岩浆历史的不同部分。这种不确定性使得很难比较不同晶体和/或来自不同火山的晶体的年龄，阻碍了我们对岩浆过程时间尺度的一般理解。在这个特殊的项目中，研究人员将通过测量两个不同系统的相同样品中锆石和斜长石的年龄来解决这个问题：新西兰塔拉韦拉火山（奥卡泰纳火山口综合体的一部分）和魔鬼山圆顶、南姐妹火山，俄勒冈州（熔岩流从复合火山）。研究计划将包括测量锆石中的238 U-230 Th年龄以及226 Ra-230 Th和238 U-230 Th年龄。两个岩浆系统中的斜长石和锆石的~（230）Th同位素年龄均呈块状分布。这些数据将提供有关的时间关系的结晶在同一系统中的主要阶段和微量阶段，并帮助划定哪些部分的岩浆历史记录的每一个mineral.A次要目标是了解Okataina和南姐妹下的岩浆存储的动态，作为一个大容量的火山口系统和小容量的火山穹隆，分别代表。总的来说，这些数据将为现有和未来的U系列晶体年龄提供一个解释性的背景，也将提供洞察岩浆在两个系统不同的喷发历史的动态。该项目将提供对解释U系列矿物年龄至关重要的数据，这将对利用这些年龄了解岩浆系统产生广泛的科学影响。Kaharoa项目将促进跨越三个机构（美国加州大学戴维斯分校;加拿大不列颠哥伦比亚省大学;新西兰坎特伯雷大学）的国际合作，因此，拟议工作的结果将与比其他方式更大的数据体相结合。

Understanding the ways in which magmas beneath volcanoes evolve, and the time scales over which they evolve, is important both in terms of gaining fundamental insights into how volcanic systems work and in terms of improving our ability to forecast volcanic eruptions. Crystals in volcanic rocks erupted at the surface contain chemical records of their interactions with magmas beneath the surface, and dating of these crystals can therefore provide information about chemical changes within the system over time. However, ages of different types of crystals (for example, zircon and plagioclase) generally yield different characteristic ages. It is unclear whether this is due to the scale of analysis (individual crystals for zircon compared to aggregates of thousands of crystals for plagioclase), due to the fact that zircon and plagioclase have typically been analyzed in different types of volcanic systems (large, caldera-forming systems for zircon, smaller systems for plagioclase), or because the two types of crystals record different parts of a magma's history. This uncertainty makes it difficult to compare ages of different crystals and/or crystals from different volcanoes, hampering our ability to develop a general understanding of the timescales of magmatic processes. In this particular project, the investigators will address this problem by measuring ages of zircon and plagioclase in the same samples for two different systems: Tarawera volcano, New Zealand (part of a the Okataina caldera complex) and Devils Hills domes, South Sister volcano, Oregon (lava flows from a composite volcano).The research plan will include measuring in situ 238U-230Th ages in zircon and 226Ra-230Th and 238U-230Th ages in bulk separates of both plagioclase and zircon from samples derived from the two magmatic systems. These data will provide information about the temporal relationship between crystallization of major and trace phases in the same system and help delineate which parts of the magmatic history are recorded by each mineral. A secondary goal is to understand the dynamics of magma storage beneath Okataina and South Sister, as representatives of a large-volume silicic caldera system and small-volume silicic domes, respectively. Collectively, these data will provide an interpretive context for existing and future U-series crystal ages, and will also provide insights into the dynamics of magmas in two systems with disparate eruptive histories. This project will provide data that are fundamental to interpretation of U-series mineral ages, which will have broad scientific impact in use of these ages to understand magmatic systems. The Kaharoa project will foster international collaborations spanning three institutions (UC Davis, US; Univ. British Columbia, Canada; and Univ. Canterbury, New Zealand) and the results of the proposed work will therefore be integrated with a much larger body of data than would otherwise be possible.