| NSF Org: |
EAR Division Of Earth Sciences |
| Recipient: |
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| Initial Amendment Date: | August 12, 2010 |
| Latest Amendment Date: | August 12, 2010 |
| Award Number: | 1019545 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Sonia Esperanca
EAR Division Of Earth Sciences GEO Directorate for Geosciences |
| Start Date: | August 15, 2010 |
| End Date: | July 31, 2013 (Estimated) |
| Total Intended Award Amount: | $109,513.00 |
| Total Awarded Amount to Date: | $109,513.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1000 E UNIVERSITY AVE LARAMIE WY US 82071-2000 (307)766-5320 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1000 E UNIVERSITY AVE LARAMIE WY US 82071-2000 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
Petrology and Geochemistry, International Research Collab |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
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.
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The goal of this research was to study the fundamental petrogenetic and magmatic differentiation processes operating in continental rear-arc regions, with a specific focus on the Northern Volcanic Zone of Ecuador. Our studies specific objective was to identify how mantle-melting, magma differentiation, crustal assimilation, and fluids and sediments addition influences the chemical compositions of the Ecuadorian rear-arc lavas, with an eye toward being able to better predict their eruptive frequency and behaviors.
Our study had three main phases:
1) Field Work: In December 2011 we spent 1 month in Ecuador collecting samples from the active volcano Reventador (3562 m) and the currently inactive volcanoes of Pan De Azucar (3482 m) and Sumaco (3990 m). Our field party included Dr. Jennifer Garrison (Cal State Los Angeles); Dr. Kennth Sims (University of Wyoming); Dr Gene Yogodzinski (University of So. Carolina); Post Doctoral Researcher Chris Waters and MSc Student Tim Matthews from the University of Wyoming; two minority undergraduate students, Ricardo Escobar and Jessica Chaney, from Cal State LA; and three students and employees of the Instituto Geofísico Escuela Politécnica Nacional in Ecuador. This field work was very successful and we collected 56 samples for analysis.
2) Analytical analyses: The samples major and trace element compositions were analyzed at WSU, which is an NSF sponsored laboratory. IN addition, their Nd, Hf, Sr, and Pb isotopic compositions and U-Th-Ra disequilibria were measured at University of Wyoming and at the ENS-Lyon France.
3) Interpretation: Our study, which has been presented in conference proceedings and is being submitted for publication in peer reviewed journals addressed the following research questions:
- What are the dominant melting processes operating in the rear-arc of the NVZ; and, is decompression melting an important process in this region?
The dominant melting process at Reventador volcano is dehydration melting related to fluids from the slab as reflected in their hydrous mineral assemblage (including hornblende). Lavas from Sumaco contain no hydrous phases, and the alkaline nature of these lavas is more typical of decompression melting than dehydration melting, and as such is more typical of ocean island basalts than subduction melting.
- What is the source of the north-south chemical variation in the rear arc; and, is there structural control on NVZ rear-arc magmatism?
The source of north-south chemical variation appears to be controlled by the geometry of the subducting slab, which likely steepens from north to south. The effect of this is that less water is available for mantle melting beneath Sumaco Volcano, which is the southern-most of the volcanoes in this study. This creates a chemical signature that is indicative of lower degrees of melting as reflected in the trace elements and U-series isotope data.
- How have magma composition and differentiation processes changed over time at Reventador and Sumaco?
The geochemical signature and mineral phases at El Reventador have not changed significantly during the time period analyzed, from 2002-2009. The ages of the lavas from Sumaco are uncertain, however the data indicate that the most recent summit lavas are significantly geochemically different than flank lavas; this is attributed to source variability and accessory phase fractionation (apatite and hauyne).
Broader Societal Impacts:
Hazards: The scientific and sociological imperatives to study Reventador have never been greater due to an eruption of the v...
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