Cenozoic crustal genesis in SW Pacific arcs and backarcs

摘要0751600(吉尔)智力价值：这项研究考察了在没有先前存在的大陆地壳的情况下，在1~5000万年的俯冲周期中，从开始到消亡，地幔和地壳是如何演化的。它涉及四个来自西南太平洋克尔马德克-斐济-汤加地区岩石的火成岩岩石学项目。将利用火山岩的地球化学和同位素特征进行测试，以回答(1)俯冲启动是否具有特征的岩浆特征和成因；(2)弧后裂谷期间地幔楔中的岩浆成因是否从熔剂主导演变为减压主导熔融；以及(3)原生弧岩浆活动的地球化学特征是否传递到具有陆相性质的第二阶段地壳。该地球化学计划包括产生和解释大量的微量元素和Nd-Hf-Sr-Pb同位素数据。此外，还将获得火成岩的U/Pb和Ar-Ar年龄，并与北半球的类似结果进行比较。第一个项目的重点是斐济和汤加最古老的岩石。第二个重点是斐济在3-5 Ma期间喷发的玄武岩，以及哈弗尔海槽的交叉链和裂谷盆地中的玄武岩。第三种是使用斐济不同年龄和成分的花岗岩，包括(U-Th)/He双重测年“。一个预期的影响将是评估地球上两个最大和研究最深入的大洋弧：伊祖-马里亚纳斯岛和克尔马德克-斐济-汤加之间的共同过程。广泛影响：所有这三个项目都直接补充了国家科学基金会资助的岛弧和弧后盆地在RIDGE 2000、CESSURES和IODP中的研究重点。它们还涉及与日本和新西兰科学家的国际合作。该项目为两名研究生和几名本科生提供教育/培训机会。公众外展和传播将通过边缘教育和外展计划进行，并将向史密森国家自然历史群岛博物馆的收藏品提供文件齐全的样本收藏，在那里将无限期地进行收藏。

ABSTRACT 0751600 (Gill)Intellectual Merit: This research examines how the mantle and crust of the Earth evolve from during one ~50 million year cycle of subduction, from initiation to demise, in the absence of pre-existing continental crust. It involves four igneous petrological projects on rocks from the Kermadec-Fiji-Tonga area of the SW Pacific. Test using the geochemical and isotopic signatures of volcanic rocks will be used to answer (1) whether subduction initiation has a characteristic magmatic signature and cause; (2) if magma genesis in the mantle wedge during back-arc rifting evolves from flux-dominated to decompression-dominated melting; and (3) whether geochemical features of primary arc magmatism get passed on to second stage" crust that is continental in character. The geochemical plan includes generation and interpretation of extensive trace element and Nd-Hf-Sr-Pb isotope data. In addition, U/Pb and Ar-Ar ages will be obtained for igneous rocks, and results compared to analogues in the northern hemisphere. The first project focuses on the oldest rocks in Fiji and Tonga. The second focuses on basalts erupted in Fiji during 3-5 Ma, and those in cross-chains and rift basins in the Havre Trough. The third uses the granitic plutons of different ages and compositions in Fiji and includes (U-Th)/He double-dating". One anticipated impact will be to assess the commonality of processes between Earth's two largest and best-studied oceanic arcs: Izu-Marianas, and Kermadec-Fiji-Tonga.Broader Impacts: All three projects directly complement the NSF-funded island arc and backarc basin research foci in RIDGE2000, MARGINS, and IODP. They also involve international collaboration with scientists in Japan and New Zealand. The project provides education/training opportunities for two graduate students and several undergraduates. Public outreach and dissemination will occur through the MARGINS Education and Outreach program and a well-documented sample collection will be provided to the Smithsonian National Museum of Natural History Islands" collection where it will be curated indefinitely.