Melt Sources and Timescales in Western Pacific Island Arcs

将对几个西太平洋岛弧（马里亚纳群岛、桑吉河[印度尼西亚]和日本）年轻火山岩的238 U和235 U衰变链中的放射性不平衡进行测量和解释。具体来说，将测量238 U-230 Th、230 Th-226 Ra和235 U-231 Pa之间的不平衡。结果将与其他地球化学数据，以获得相同的岩石，特别是微量元素浓度测量的ICPMS和Sr-Nd-Pb同位素比值测量的TIMS。这些补充可以识别可能在岩浆源区的成分。特别注意将放在确定结果是否限制熔化的物理过程（如孔隙度，上涌速率和地幔的熔体生产力之间的弧和俯冲岩石圈的楔），因为是在行星岩浆活动的其他主要网站的情况下。预计这种过程在俯冲带会有所不同，在俯冲带，熔融是通过俯冲沃茨的流动发生的，而且可能快得多。另一种选择是放射性不平衡也由源成分主导。 通过比较三个不同的弧的结果，我们将探讨不同的构造环境和源成分的作用。 日本的结果将与世界上最好的融化地震层析成像相结合，但也有必要与熟悉正在研究的火山的日本同事密切合作，以便充分考虑到当地的地质背景。结果将通过加州K12合作计划的大学传播。

GillEAR-0106206Radioactive disequilibria in the 238U and 235U decay chains will be measured and interpreted for young volcanic rocks from several western Pacific island arcs (Marianas, Sangihe [Indonesia], and Japan). Specifically, disequilibria between 238U-230Th, 230Th-226Ra, and 235U-231Pa will be measured. Results will be integrated with other geochemical data to be obtained for the same rocks, especially trace element concentrations measured by ICPMS and Sr-Nd-Pb isotope ratios measured by TIMS. These supplemental can fingerprint components which may be in the source region of the magmas. Special attention will be placed on determining whether results constrain the physical processes of melting (such as the porosity, upwelling rate, and melt productivity of mantle in the wedge between the arc and underlying subducting lithosphere), as is the case in other major sites of planetary magmatism. Such processes are expected to differ in subduction zones where melting occurs by fluxing from subducted waters and may be much faster. The alternative is that the radioactive disequilibria are dominated by the source components too. By comparing results from three quite different arcs, we will explore the role of different tectonic environments and source components. Results for Japan will be integrated with seismic tomographic images of melting there, which are the best in the world, but it will also be necessary to work closely with Japanese colleagues familiar with the volcanoes being studied in order to take the local geological context fully into account. Results will be disseminated through a University of California K12 partnership program.