Rates, Sources and Magmagenesis of Alkalic Lavas at the Edge of an Intraplate Hotspot: A Multi-tracer Study of the Youngest Volcanics on Oahu, Hawaii

板内热点边缘碱性熔岩的速率、来源和岩浆成因：夏威夷欧胡岛最年轻火山的多示踪剂研究

• 批准号: 0838271
• 负责人: Kenna Rubin
• 金额: $ 29.77万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-01-15 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838271&HistoricalAwards=false
• 关键词: Rates; Sources; Magmagenesis; Alkalic; Lavas

Intellectual Merit. Late-stage, alkalic magmatism at mid-plate hotspots is an enigmatic occurrence that is poorly understood. Geochemical models suggest that magma genesis is strongly dominated by melts of metasomatised lithospheric mantle, whereas most geophysical models require buoyant upwelling in the asthenospheric mantle. Neither model predicts the full range of observations of time, composition and geology in the volcanic deposits. This proposal addresses multiple outstanding questions to inform models for alkalic rejuvenation volcanism, occurring far downstream of the primary locus of active mid-plate hot spot volcanism.1. What causes the magma production that feeds late stage alkalic rejuvenation volcanism?2. Are rejuvenation volcanics formed primarily by melting the lithosphere or the asthenosphere?3. Are the lithospheric lithologies possibly involved in petrogenesis old or young?4. What are the length and temporal scales of heterogeneity in sources or melting processes?5. What magmatic plumbing conditions allow extreme compositional heterogeneity in erupted lavas over short time and length scales?The Honolulu Series volcanics on Oahu, Hawaii serves as a case study of the causes and conditions of alkalic rejuvenation volcanism. This project focuses on its last two eruption sequences (the subaerial Tantalus rift and the submarine/subaerial Koko rift) because they exhibit the extreme compositional range within Honolulu Series volcanism (and elsewhere), there isstrong geologic control (nearly contemporaneous volcanism at multiple vents along each rift), and eruption ages young enough (80 ka) to constrain rates and timing of igneous processes with 230Th-238U and 231Pa-235U disequilibria. Moreover, samples are fresh and previously have been well characterized.U-series disequilibria can distinguish syn- and recent premagmagenetic chemical fractionation in melts and sources to determine when they occurred. A pilot project to determine the age of Koko rift zone volcanism from recrystallized coral xenoliths also produced preliminary U-series analyses of lavas that show extensive 230Th-238U disequilibria. The relative youth, great distance from the active hotspot (340 km), and other attributes make these eruptions exceptional examples for a detailed study about sources and styles of magmatism at what is effectively a type-locality for intra plate alkalic volcanism. The project will involve samples already in hand, including legacy samples studied by Jackson, Clague and Frey, provided by the Smithsonian Institution and submarine Koko samples provided by Dave Clague. The project will primarily utilize existing analytical expertise (U-series, Sr-Nd-Pb-Os isotopes, major and trace elements) and instrumentation in the UH laboratories, but also includes 231Pa methods development to be used in this and subsequent research.Broader Impacts. This project will contribute to development of new US research capabilities for measuring 231Pa-235U radioactive disequilibrium to study volcanic systems. It will also facilitate transition of analytical methods to new instrumentation and development of an early career post-doctoral researcher. Results of this project will be disseminated in peer-reviewed literature, incorporated in university courses, made available to the public via the award winning Hawaii Center for Volcanology website (created/maintained by PI Rubin), and added to a visitors center display about Koko Rift volcanism for the internationally renowned Hanauma Bay beach park.

智力优点。中板热点处的后期，碱性岩浆作用是一种神秘的事件，人们理解很少。地球化学模型表明，岩浆起源是由岩石圈地幔的融化而强烈控制的，而大多数地球物理模型都需要在进行软层地幔中浮动的上升。这两个模型都可以预测火山沉积物中时间，组成和地质的全部观察。该提案解决了多个杰出的问题，以告知模型的碱性恢复火山，这是在主动中板热点火山的主要基因座的下游发生的。1。是什么原因导致岩浆产量为后期的碱性恢复火山作用？2。恢复火山是主要是通过熔化岩石圈或软圈融化而形成的？3。岩石圈岩石学是否可能参与古老或年轻的岩石发生？4。源或熔化过程中异质性的长度和时间尺度是什么？5。哪些岩浆管道条件允许在短时间内爆发的熔岩中极端组成异质性？ This project focuses on its last two eruption sequences (the subaerial Tantalus rift and the submarine/subaerial Koko rift) because they exhibit the extreme compositional range within Honolulu Series volcanism (and elsewhere), there isstrong geologic control (nearly contemporaneous volcanism at multiple vents along each rift), and eruption ages young enough (80 ka) to constrain rates and timing of igneous 230th-238U和231Pa-235U的过程不平衡。此外，样品是新鲜的，以前已经表征了很好的表征。U系列不平衡可以区分熔体和来源中的合成和近期的前磁性化学分馏，以确定它们何时发生。一个试点项目，以确定重结晶的珊瑚异种石的Koko Rift区火山的年龄，还产生了对熔岩的初步U系列分析，这些分析表现出广泛的230th-238U不平衡。相对青年，与活跃的热点（340公里）的距离很远，以及其他属性，使这些爆发使有关岩浆岩岩岩内碱性火山的类型局部性的详细研究进行了详细研究。该项目将涉及已经掌握的样品，包括杰克逊，克拉格和弗雷研究的遗产样品，该样本由史密森尼机构提供，以及由戴夫·克拉格（Dave Clague）提供的潜艇Koko样品。该项目将主要利用UH实验室中的现有分析专业知识（U系列，SR-ND-PB-OS同位素，主要和微量元素）和仪器化，但还包括231PA方法开发，可用于此研究以及随后的研究。 该项目将有助于发展美国新的研究能力，以测量研究火山系统的231PA-235U放射性不平衡。它还将促进分析方法向新仪器的转变，并开发早期职业生涯后研究人员。该项目的结果将在经过同行评审的文献中传播，并在大学课程中纳入，并通过获奖的夏威夷火山学中心网站（由Pi Rubin创建/维护）提供给公众，并添加到了访客中心展示的有关Koko Rift Volcanism的国际票房式Hanauma Bay Beach Beach Park。