Production and Ascent of Magma at Convergent Margins: Information From Small Eruptive Centers in the Central Southern Volcanic Zone, Chile

9725366 Hickey-Vargas拟议的研究是对智利南部火山带（CSVZ）中部小型喷发中心的玄武质火山岩进行地球化学研究。 与玄武岩复合成层火山在CSVZ，断层对齐的小中心定义了一个空间和地球化学模式，这表明他们形成了广泛的熔融，但系统地变化量的含水俯冲相关的流体。 这项研究的目的是检验关于岩浆从俯冲板块上方熔融和上升的相互竞争的假设。地球化学和同位素数据将用于确定含水流体成分的数量与熔融程度之间的关系。 10 Be和238 U/230 Th的活性比将被确定为选定的样品，并与现有的数据进行比较，从复合成层火山，以确定是否玄武岩从小中心包括较少量的最近提取的岩石圈。斑晶矿物的岩相学和电子探针分析将用于推断液体成分。 这项研究的结果将通过有助于我们理解会聚边缘岩浆活动，特别是通过确定一些大小火山中心选址的控制因素，确定俯冲带岩浆的来源以及地幔和地壳之间循环某些元素的途径来推进知识。 此外，这项研究将通过培养一名博士生来促进教育。学生，并促进美国和智利科学家之间的合作。

9725366 Hickey-Vargas The proposed research is a geochemical study of basaltic volcanic rocks from small eruptive centers in the central Southern Volcanic Zone (CSVZ), Chile. Together with basalts from composite stratovolcanoes in the CSVZ, the fault-aligned small centers define a spatial and geochemical pattern suggesting that they were formed by melting with widely, but systematically varying amounts of hydrous subduction-related fluids. The objective of the research is to test competing hypotheses for melting and ascent of magma from above the subduction plate. Geochemical and isotopic data will be used to determine the relationship between the amount of hydrous fluid component and extent of melting. 10Be and 238U/230Th activity ratios will be determined for selected samples and compared with existing data from the composite stratovolcanoes, to determine whether basalts from the small centers include smaller amounts of recently extracted lithosphere. Petrography and electron microprobe analyses of phenocryst minerals will be used to infer liquid compositions. The results of this research will advance knowledge by contributing to our understanding of convergent margin magmatism, specifically, by identifying some of the controls on the siting of large and small volcanic centers, defining sources of subduction zone magma, and the pathways for cycling some elements between mantle and crust. Further, the research will advance education through the training of one Ph. D. student, and promote collaboration between U.S. and Chilean scientists.