Collaborative Research: Rear-arc Magmatism in the Northern Volcanic Zone of the Andes: Processes and Timescales in a Continental Rear-arc Setting

合作研究：安第斯山脉北部火山带的弧后岩浆作用：大陆弧后环境中的过程和时间尺度

• 批准号: 1019545
• 负责人: Kenneth Sims
• 金额: $ 10.95万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-08-15 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1019545&HistoricalAwards=false
• 关键词: Collaborative; Research; Rear; arc; Magmatism

The overarching goal of this research is to investigate rear-arc petrogenetic processes in the Northern Volcanic Zone (NVZ) of the South American Andes. The NVZ is ideal for this study because it is similar in many ways to other well-studied arcs, yet it exhibits characteristics that are unique to the NVZ. This research is important because we have the opportunity to learn about the processes that mark the transition from dominantly subduction-influenced melting to the regime of MORB-type petrogenesis in South America. In addition to the primary objective, timescales will be evaluated for magma ascent and degassing in an active, calc-alkaline rear-arc volcano (El Reventador), which is important for constraining the timescales of magmagenesis in the rear-arc region. The new data set will be used to test existing models of rear-arc magmatism, while developing new models that can be applied to future arc research.The proposed research will comprise a regional, in-depth, geochemical study of Ecuadorian rear-arc volcanoes using a combination of field research, analytical work and geochemical modeling. Petrogenetic processes will be characterized using major and trace elements combined with radiogenic isotopes (Pb, Sr, Nd) and U-series on whole rocks and mineral separates. Special attention will be given to minerals in order to characterize melt inclusions and compositional variation that reveal fine-scale petrogenetic fingerprints. Timescales (i.e. crystallization and degassing rates, ages) will be determined by measuring 238U-, 230Th-, 226Ra, and 210Pb- and 210Po nuclides in mineral separates and whole rocks, using facilities at WHOI and the Universities of Wyoming and Iowa. Rigorous characterization of minerals and will be accomplished using electron microprobe and secondary ion mass spectrometry facilities at UCLA. These data will be used to evaluate contrasting models for melt formation.Intellectual Merit. This research is critical for understanding the nature of rear-arc processes in the Andean continental arc and arcs in general. The uniqueness of the NVZ lies in the compositional diversity of magmas (calc-alkaline and alkaline), the location of the rear-arc at the boundary of the South American craton, and the (possible) influence of the subducting Carnegie Ridge. Similarities to other rear-arc volcanoes provide a strong foundation for comparing our data and testing models. The application of U-series nuclides to igneous geochemistry has proven useful for determining melting and differentiation timescales in arc volcanoes, and more recently for identifying melting and differentiation processes. These currently active volcanoes in Ecuador present an opportunity to use U-series nuclides to investigate melting processes and magmatic timescales in a rear-arc setting.Broader Impacts. The Broader Impacts of this project include promoting geoscience to students, fostering international communication and emphasizing the importance of science to society. Incorporation of an interactive website as part of the field research, will bring the field experiences directly into classrooms in the U.S. and Ecuador, and provide students a sense of scientific discovery that could have a long lasting and positive impact on their lives. This project has the potential to strengthen the scientific foundation of K-12 students, with a large impact on minority students in a dominantly Hispanic community. Additionally, this funding will support a graduate student and provide funding for a junior faculty member at California State University, Los Angeles.--

这项研究的总体目标是研究南美安第斯山脉北部火山区（NVZ）的后弧质发生过程。 NVZ是这项研究的理想选择，因为它在许多方面与其他经过良好的弧线相似，但是它具有NVZ独有的特征。这项研究很重要，因为我们有机会了解从受俯冲影响的融化到南美病态质发生的状态的过渡。除了主要目标外，还将评估岩浆上升和脱气的时间尺度，并在一个活跃的钙碱后弧火山（El Reventador）中进行脱气，这对于约束后部ARC区​​域岩浆的时间表很重要。新的数据集将用于测试现有的后弧岩浆模型，同时开发可应用于未来的ARC研究的新模型。拟议的研究将包括对厄瓜多尔后弧火山的区域，深入的，地球化学研究，使用现场研究，分析工作和地球化学模型的组合。将使用主要和微量元素结合放射性同位素（PB，SR，ND）和整个岩石和矿物分离的U系列来表征岩发生过程。将特别注意矿物质，以表征熔体夹杂物和构成变化，揭示了细质岩发生指纹。时间尺度（即结晶速率，年龄）将通过测量矿物质和整个岩石中的238U-，230th-，226ra和210pb-和210pb-和210po核的确定，并使用WHOI和WYOMINIT和IOWA大学的设施使用设施。矿物质的严格表征将使用UCLA的电子微探针和二级离子质谱设施来完成。这些数据将用于评估熔体形成的对比模型。这项研究对于理解安第斯大陆弧和弧线中后弧过程的性质至关重要。 NVZ的独特性在于岩浆的组成多样性（钙碱和碱性），后弧在南美克拉顿边界的位置以及俯冲卡内基山脊的（可能的）影响。与其他后弧火山的相似之处为比较我们的数据和测试模型提供了坚实的基础。事实证明，将U系列核素应用于火成岩地球化学，可用于确定弧火山中的熔化和分化时间尺度，而最近又用于识别熔融和分化过程。这些目前在厄瓜多尔的活跃火山提供了使用U系列核素在后弧形环境中研究熔化过程和岩浆时尺度的机会。该项目的更广泛的影响包括促进对学生的地球科学，促进国际交流并强调科学对社会的重要性。将互动网站纳入了现场研究的一部分，将把现场体验直接带入美国和厄瓜多尔的教室，并为学生提供一种科学发现感，可能会对他们的生活产生持久和积极的影响。该项目有可能加强K-12学生的科学基础，对主要是西班牙裔社区中的少数族裔学生产生了巨大影响。此外，这笔资金将支持一名研究生，并为洛杉矶加利福尼亚州立大学的一名初级教职员工提供资金。