Melt Sources and Timescales in Western Pacific Island Arcs

238U和235U衰变链中的放射性不平衡将在几个西太平洋岛弧（马里亚纳、桑吉河[印度尼西亚]和日本）的年轻火山岩中进行测量和解释。具体来说，将测量238U-230Th， 230Th-226Ra和235U-231Pa之间的不平衡。结果将与同一岩石的其他地球化学数据相结合，特别是ICPMS测量的微量元素浓度和TIMS测量的Sr-Nd-Pb同位素比值。这些补充成分可能是岩浆源区的指纹成分。将特别注意确定结果是否限制了熔融的物理过程（如孔隙度、上升流速率和地幔在弧和下伏的俯冲岩石圈之间的楔块中的熔融率），就像在其他主要的行星岩浆活动地点的情况一样。这种过程预计在俯冲带会有所不同，在俯冲带，融化是通过俯冲水的流动发生的，而且可能要快得多。另一种选择是，放射性不平衡也受源成分的支配。通过对比三个完全不同的弧的结果，我们将探讨不同构造环境和源组分的作用。日本的结果将与世界上最好的火山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，以便充分考虑当地的地质背景。结果将通过加州大学K12合作项目传播。

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.