Melt Sources and Timescales in Western Pacific Island Arcs

GILLEAR-0106206 238U和235U衰变链中的放射性不平衡将被测量并解释来自几个西太平洋岛弧(马里亚纳群岛、三吉河岛[印度尼西亚]和日本)的年轻火山岩。具体来说，将测量238U-230Th、230Th-226Ra和235U-231Pa.结果将与将获得的相同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测量的锶-钕-铅同位素比值。这些补充可以对可能位于岩浆源区的成分进行指纹识别。将特别注意确定结果是否像行星岩浆活动的其他主要地点那样限制了熔融的物理过程(如弧形和下伏岩石圈之间的楔形区地幔的孔隙度、上升率和熔体生产力)。这样的过程在俯冲带预计会有所不同，在那里，熔化是通过从俯冲水域熔化而发生的，而且可能会快得多。另一种选择是，放射性不平衡也是由源成分主导的。通过比较来自三个完全不同的弧段的结果，我们将探索不同的构造环境和源区成分的作用。日本的结果将与世界上最好的日本熔化的地震层析成像图像相结合，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。结果将通过加州大学K12合作项目进行传播。

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.