238U and 232Th Series Studies of Arc-related Magmas

本文用~(238)U和~(232)Th衰变系列系统学方法研究了火山弧壳地幔层次的岩浆作用。部分资金将用于完成正在进行的项目，这些项目侧重于在喀斯喀特弧形火山中产生和积累流纹岩所需的过程和时间长度。正在研究的火山(梅迪奇湖和火山口湖)在全新世喷发了硅质岩浆，并通过美国地质调查局合作者的工作在地质和地球化学方面广为人知。大约需要6-9个月的时间来完成对全岩和所含矿物相的核素活动的分析，用开放系统模拟技术确定岩浆停留时间，并写出结果。两年研究期的剩余时间将用于调查镁铁质岩浆的起源，这些镁铁质岩浆是中美洲弧状岩浆系统的地球化学和热学母体。我们将分析来自中美洲弧的20-25块岩石和科科斯板块的沉积物，以确定238U-230Th-226Ra-232Th的活动。其他科学家正在对这些岩石进行10Be/Be比值、锶、钕和铅同位素比值以及硼、微量元素和常量元素浓度的分析。其目的是描绘中美洲弧状岩浆中俯冲板块成分的性质，它参与弧状岩浆成因的方式，以及岩浆产生和运输所需的时间尺度。

This is study of magmatic processes occurring at crust and mantle levels in volcanic arcs using 238U and 232Th decay series systematics. Part of the funding will be used to complete ongoing projects that focus on the processes and lengths of time required to generate and accumulate rhyolite in Cascade arc volcanoes. The volcanoes that are being studied (medicine Lake and Crater Lake) have erupted silicic magmas in the Holocene, and are well-known geologically and geochemically through the work of U.S.G.S. collaborators. Approximately 6-9 months will be necessary to complete the analyses of whole rocks and contained mineral phases for nuclide activities, to determine magma residence times with open-system modeling techniques, and to write up the results. The remainder of the 2-year study period will be used to investigate the origin of mafic magmas that are the geochemical and thermal parents of Central American arc magma systems. We will analyze 20-25 rocks from the Central American arc and sediments from the Cocos Plate for 238U-230Th-226Ra-232Th activities. These same rocks are being analyzed by other scientists for 10Be/Be ratios, Sr, Nd, and Pb isotopic ratios, and B, trace element, and major element concentrations. The goal is to delineate the nature of the subducting slab component in Central American arc magmas, the way it becomes involved in arc magma genesis, and the time scales required for magma generation and transport.