Generation of Basaltic and Andesitic Magma in the Central Southern Volcanic Zone, Chile

将以智利安第斯中南部火山带为天然实验室，研究大陆汇聚边缘玄武岩和安山岩的岩浆成因。需要解决的问题是：1)弧下地幔楔体如何同时产生不同的玄武岩岩浆？安山质岩浆是如何在大陆弧背景下由玄武岩岩浆生成的？基于以前工作的一种假设，即大型玄武岩层状火山是由地幔楔体的熔融产生的，而小喷发中心(SEC)是经过俯冲修改的地幔楔体的减压熔体，这一假说将得到验证。将对玄武岩进行流动元素(B、Sb、Mo、Sn)和U系列同位素(230Th、226Ra、238U、232Th)的分析。将对橄榄石中的熔融包裹体进行挥发性元素(水、二氧化碳、氯、S、F)的分析。这些结果将有助于确定熔融过程中的楔体成分，以及玄武岩岩浆熔融和上升的时间。来自两个火山中心的安山岩，将通过电子探针、离子探针和激光烧蚀ICPMS对矿物、基质和熔体包裹体进行分析，研究脱气岩浆低压分离结晶和地壳同化和角闪石结晶的块状岩石趋势。U系列同位素将在选定的玄武岩-安山岩对中进行研究，以比较不同分异过程的时间。这些结果将有助于理解大陆弧中岩浆的形成，并有助于基本的地质/地球化学问题，如俯冲物质向地幔楔体和大陆地壳的质量转移的过程和时间尺度。作为该项目的一部分，FIU将开发一个用于收集SVZ岩石样本的基于互联网的岩石学和化学数据数据库，研究将使FIU的本科生参与正在进行的NSF资助的项目，以增强地球科学的多样性。国际和平协会和学生将参加2004年在智利普肯举行的IAVCEI大会，并与智利同事进行进一步的研究互动。

The petrogenesis of basaltic and andesitic magma at continental convergent margins will be investigated using the Andean Central Southern Volcanic Zone, Chile, as a natural laboratory. Problems to be addressed are: 1) How are diverse basaltic magma generated concurrently from the sub-arc mantle wedge? and 2) How is andesitic magma generated from basaltic magma in a continental arc setting? A hypothesis, based on previous work, that large basaltic stratovolcanoes are generated by flux melting of the mantle wedge, whereas small eruptive centers (SEC) are decompression melts of "aged" subduction-modified mantle wedge, will be tested. Basaltic rocks will be analyzed for fluid-mobile elements (B, Sb, Mo, Sn), and U-series isotopes (230Th, 226Ra, 238U, 232Th). Melt inclusions in olivines will be analyzed for volatile elements (H2O, CO2, Cl, S, F). These results will help to determine the wedge composition during melting, and the timing of melting and ascent of basaltic magma. Andesites from two volcanic centers, exhibiting contrasting bulk rock trends of low-pressure fractional crystallization of degassed magma and crustal assimilation and hornblende crystallization, will be examined through analysis of minerals, groundmass and melt inclusions using electron microprobe, ion-microprobe and laser ablation ICPMS. U-series isotopes will be studied in selected basalt-andesite pairs to compare the timing of distinct differentiation processes. Results will contribute to an understanding of magma generation in continental arcs, and to fundamental geologic/geochemical issues such as the processes and time scales for mass transfer of subducted materials to the mantle wedge and to the continental crust. An internet-based database of petrographic and chemical data for the collection of SVZ rock samples housed at FIU will be developed as part of this project, and research will integrate FIU undergraduates participating in an ongoing NSF-funded project to enhance diversity in the geosciences. The PI and students will attend the 2004 IAVCEI General Assembly in Pucon, Chile, and further research interactions with Chilean colleagues.