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

University Of Wyoming, Laramie WY

Investigators

Abstract

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. --