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，研究大陆辐合边缘玄武岩和安山岩岩浆的岩石成因。需要解决的问题有：1)弧下地幔楔如何同时产生多种玄武岩岩浆？2)大陆弧环境下，安山岩岩浆是如何从玄武岩岩浆中生成的？一个基于先前工作的假设，即大型玄武岩层状火山是由地幔楔的通量熔融产生的，而小型喷发中心（SEC）是“老化”俯冲修正的地幔楔的减压熔体，将被验证。玄武岩将分析流体流动元素（B, Sb, Mo, Sn）和u系列同位素（230Th, 226Ra, 238U, 232Th）。将分析橄榄石中的熔体包裹体中的挥发性元素（H2O, CO2, Cl， S， F）。这些结果将有助于确定熔融过程中的楔块成分，以及玄武岩岩浆的熔融和上升时间。本文将利用电子探针、离子探针和激光烧蚀ICPMS对两个火山中心的安山岩进行矿物、地质体和熔体包裹体的分析，研究安山岩在脱气岩浆低压分异结晶、地壳同化和角闪石结晶等方面的大块岩石特征。u系列同位素将在选定的玄武岩-安山岩对中进行研究，以比较不同分化过程的时间。结果将有助于理解大陆弧的岩浆生成，以及基本的地质/地球化学问题，如俯冲物质向地幔楔和大陆地壳的质量传递过程和时间尺度。作为该项目的一部分，将开发一个基于互联网的岩石学和化学数据数据库，用于收集存放在FIU的SVZ岩石样本，研究将整合FIU本科生参加正在进行的美国国家科学基金会资助的项目，以增强地球科学的多样性。PI和学生将参加在智利普孔举行的2004年IAVCEI大会，并与智利同事进一步进行研究交流。

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.