Rapid cycling of magma compositions in continental arc systems

William Marsh Rice University, Houston TX

Investigators

Abstract

This project aims to characterize timescales associated with changes in the chemical composition of volcanoes that erupt on the edges of continents where one tectonic plate dives beneath another (i.e., subduction zones). Understanding timescales for chemical changes will provide insights into magma systems that feed volcanic eruptions. This project will focus on the question of whether the chemistry of volcanic systems in subduction zones can change on timescales less than 100,000 years. In order to answer this question, this project will investigate a sequence of volcanic ash derived from volcanoes that erupted along the west coast of the US over 65 million years ago and was deposited in west Texas over a 7-million-year period. Major goals of the project include creating a high-resolution record of volcanic composition to better understand how and why volcanism changes over time. In addition to filling important gaps in current understanding about volcanoes and magmatic systems, this project will also have implications for understanding the generation of strategic natural resources that will be critical for the energy transition to from hydrocarbons to a more renewable energy base. In particular, insights into copper and lithium deposits may arise from this project. Part of this project will also involve developing a course on the science, economics, and policy of natural resources, which will help educate earth scientists on the natural resources necessary for the energy transition. Continental arc volcanism generates a wide diversity of magma compositions, but the tempos of compositional variation are unclear. Understanding how the average composition of arc magmas varies in space and time may provide insights into the physics of the transcrustal magmatic system in arc settings. This project focuses on the fundamental question of whether the composition of a magmatic arc can systematically change on timescales of less than 10-100 kyr. A high-resolution record of ash that has been altered into bentonite will enable reconstruction of a detailed history of arc composition. Four major goals will contribute to answering this question. The first goal is to examine diagenetic signals in bentonites in order to assess elemental mobility during bentonite formation. The second goal involves reconstructing ash protolith compositions from the altered bentonites in order to create a record of arc composition over time. A third goal is to analyze volcanic minerals for additional petrogenetic signals to inform about magmatic processes. Results from these first three goals will enable models of how magmatic flux, erosion, tectonism, and crustal thickness influence timescales and processes of transcrustal magma and heat transfer. Methods will include using μXRF for compositional mapping of bentonites, ICPMS for trace element analyses of bentonites, and EPMA analyses of volcanic mineral compositions. In addition to addressing the fundamental question, this project will also have implications for understanding natural resources such as Li and Cu, for understanding surface and depositional processes, and for understanding the biogeochemical and environmental impacts of volcanic ash. Broader societal impacts will include student participation in a project to improve the accessibility of urban parks and development of a course on critical mineral resources. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.