U-Series Crystal Ages and Implications for Magma Dynamics

U 系列晶体年龄及其对岩浆动力学的影响

• 批准号: 0738749
• 负责人: Kari Cooper
• 金额: $ 20.03万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-15 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738749&HistoricalAwards=false
• 关键词: Series; Crystal; Ages; Implications; Magma

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.

了解火山下的岩浆的发展方式以及它们进化的时间尺度在获得对火山系统如何工作以及提高我们预测火山喷发的能力方面的基本见解方面都很重要。在表面爆发的火山岩中的晶体包含其与表面下面的岩浆相互作用的化学记录，因此这些晶体的日期可以随着时间的推移提供有关系统内化学变化的信息。但是，不同类型的晶体的年龄（例如，锆石和斜长石）通常会产生不同的特征年龄。目前尚不清楚这是否是由于分析的规模（锆石的单个晶体与数千个斜长石的聚集体相比），这是因为通常在不同类型的火山系统中分析了锆石和斜长石（通常在不同类型的火山系统中分析了Zircon，Zircon-for Zircon-for plagioclase的较小型号），或者是两种类型的晶体，或者是两种类型的晶体，因为较大的含量）。这种不确定性使得很难比较来自不同火山的不同晶体和/或晶体的年龄，从而阻碍了我们对岩浆过程时间表的一般理解的能力。 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-230和238U-230年龄在斜长石和锆石的散装中与来自两个岩浆系统的样品分开。这些数据将提供有关同一系统中主要相结晶和微量阶段结晶之间的时间关系的信息，并帮助描绘每个矿物记录岩浆历史的哪些部分。 第二个目标是了解Okataina和South Sisters下方的岩浆存储的动力学，分别是大容量的硅细胞系统和小体积硅圆顶的代表。总的来说，这些数据将为现有和未来的U系列晶体时代提供解释性环境，还将在两个具有不同爆发历史的系统中对岩浆动态的见解。该项目将提供对U系列矿物年龄解释至关重要的数据，这些数据将在使用这些年龄来了解岩浆系统的使用方面具有广泛的科学影响。 Kaharoa项目将促进涵盖三个机构（UC Davis，美国；加拿大不列颠哥伦比亚省；和新西兰的坎特伯雷大学）的国际合作，因此，拟议工作的结果将与更多的数据集成到其他可能的数据。