Petrology of Southern Valu Fa Ridge Lavas

地壳、地幔和海洋之间的挥发分和其他化学元素的交换驱动着大气和海洋的组成，并告诉我们许多关于俯冲、地幔不均匀和其他地球深处过程的信息。这项研究利用一艘澳大利亚考察船最近沿着西太平洋的Value Fa Ridge及其相关的弧后收集的玻璃状海底火山熔岩的化学成分，来评估地幔来源成分的性质和变异性，包括与弧有关的流体和母质岩浆。样品来自刘盆地NSF资助的综合研究地点附近的一个地区，那里的俯冲和地幔过程目前正在紧张地研究中。瓦卢法山脊位于汤加王国内东刘传播中心的南端。瓦卢法山脊很重要，因为它正在迅速向南扩散，形成新的深水火山系统，逐渐接近托夫亚(汤加)火山弧的“火环”火山。这种快速的演化为研究弧后火山系统提供了一个独特的机会。这项研究包括完成熔岩玻璃的主要元素和微量元素分析，这些玻璃是从沿着瓦卢法海脊的密集横断面上从海底挖出的。广泛的挥发物(H2O、CO2等)并将对伴生同位素进行分析和解释。国际合作者将免费分析和提供同位素数据。地球化学数据将能够绘制关键元素和元素比率的分布图，这些元素和元素比率可以诊断关键的地幔来源特征和成分。这种来源物质的潜在来源包括深海沉积物和来自俯冲洋壳的海水蚀变的火山岩；在一个独特的熔融区形成的富含水和二氧化碳的流体或熔岩物质，为“火环”火山提供物质；以及在俯冲开始之前存在的“原始”地幔物质。这项研究涉及的问题是：(1)岩浆形成的深度、温度和压力是什么？(2)该地区熔融的地幔物质的化学和矿物成分是什么？(3)熔体形成时存在多少水、二氧化碳和其他挥发性物质，挥发物在熔融过程中扮演什么角色？(4)物质在多大程度上来自熔融区俯冲的洋壳？(5)这些特征是如何沿沃法海脊变化的？更广泛的影响这项研究的结果将完全整合到NSF资助的Ridge 2000综合研究场地研究中。这项工作还将支持一名研究生和本科生，他们都将接受地球化学分析方面的培训。它还将支持美国国家科学基金会资助的俄勒冈州立大学的分析基础设施。在传播成果方面，将向Ridge 200办事处提供材料，用于以刘盆地为重点的教育和外联活动。所有的地球化学数据都将提交给Ridge 2000研究数据库。这项工作还与来自澳大利亚、德国、汤加和其他南太平洋岛国的科学家进行了国际合作。

Exchange of volatiles and other chemical elements between the earth's crust, mantle, and ocean drive the composition of the atmosphere and ocean and tell us a great deal about the processes of subduction, mantle heterogeneity, and other deep earth processes. This research uses the chemistry of glassy seafloor volcanic lavas, recently collected by an Australian research vessel along the Valu Fa Ridge and its associated back arc in the western Pacific Ocean, to evaluate the nature and variability of mantle source components including arc-related fluids and parental magmas. Samples come from an area that is adjacent to the NSF-funded Integrated Study Site in the Lau Basin where subduction and mantle processes are presently under intense study. The Valu Fa Ridge lies at the southern end of the East Lau Spreading Center within the Kingdom of Tonga. The Valu Fa Ridge is important because it is rapidly propagating southward, creating new, deep-water volcanic systems that become progressively closer to the "ring-of-fire" volcanoes of the Tofua (Tonga) volcanic arc. This rapid evolution provides a unique opportunity to investigate a back-arc volcanic system, as it evolves. This research involves completing major and trace element analyses of glasses from lavas that have been dredged from the seafloor from a closely spaced transect along the Valu Fa Ridge. A wide suite of volatiles (H2O, CO2, etc.) and companion isotopes will be analyzed and interpreted. Isotope data will be analyzed and provided by international collaborators at no cost. Geochemical data will allow mapping of the distribution of key elements and element-ratios that are diagnostic of the key mantle source characteristics and components. Potential sources for this source material include deep-sea sediments and seawater-altered volcanic rocks from subducted ocean crust; water- and carbon dioxide-rich fluids or molten rock material formed in a distinct melting region that supplies the "ring-of-fire" volcanoes; and "original" mantle material that was present before subduction began. Questions addressed by this study are: (1) At what depth, temperature, and pressure are magmas forming?; (2) What is the chemical and mineralogical composition of melting mantle material in the area?; (3) How much water, carbon dioxide, and other volatile species are present when melts are formed and what is the role of volatiles in the melting process?; (4) To what extent is material derived from the subducted ocean crust in the melting region?; and (5) How do these characteristics vary along Valu Fa ridge? Broader ImpactsResults from this research will be fully integrated into NSF-funded RIDGE 2000 Integrated Study Site research. The work will also support a graduate and undergraduate student, both of whom will be trained in geochemical analyses. It will also support NSF-funded analytical infrastructure at the Oregon State University. In terms of dissemination of results, material will be provided to the RIDGE 200 office for education and outreach activities focusing on the Lau Basin. All geochemical data will be submitted to the RIDGE 2000 research database. The work also engages international collaboration with scientists from Australia, Germany, Tonga and other southern Pacific island nations.