Collaborative Research: The Proterozoic ophiolite record of ancient seafloor hydrothermal alteration and marine chemistry

California Institute Of Technology, Pasadena CA

Investigators

Abstract

Studying how the ocean and atmosphere have changed over Earth’s history helps us understand past climate and environment, as well as the development of life. Ancient pieces of ocean floor provide one way to study ancient ocean chemistry as the rocks in them have interacted with seawater. This project will investigate three pieces of ocean floor from a time between 750 million and 2 billion years ago, which is not well understood. Iron, strontium, and oxygen in these rocks will be analyzed to quantify past oxygen levels and the composition of seawater. Additionally, a detailed database of chemical data from ophiolites of all ages will be created for future research. This project supports a graduate student and offers internships to both international undergraduates and high school students from the Pasadena Unified School District. An interdisciplinary workshop will be held to share and synthesize state-of-the-art research and encourage future collaborations. In summary, this research will advance our knowledge of Earth’s early environment, with potential implications for predicting future environmental changes, and support the training of the future scientific workforce. Altered oceanic crust provides an archive to reconstruct the chemical evolution of the ocean and atmosphere over Earth’s history. During formation and cooling, oceanic crust is hydrothermally altered via low- and high-temperature interactions with seawater. These interactions modify the original composition of magmatic crust and provide a record of deep ocean seawater chemistry. Although these alteration processes are well-documented in the modern (through drilled oceanic crust) and Phanerozoic (through ophiolites, or preserved fragments of oceanic crust), the Precambrian record of oceanic chemistry is debated and poorly studied from the perspective of altered oceanic crust. This research will investigate hydrothermal alteration processes in three near-complete Proterozoic ophiolites via systematic sampling and analysis of samples from all stratigraphic levels. Specifically, bulk-rock Fe3+/ΣFe, 87Sr/86Sr, and 18O/16O will be measured to reconstruct past marine O2 concentrations, radiogenic Sr isotopic composition, and O isotopic composition. The sample suites will be archived and made available to future researchers to understand other aspects of Proterozoic marine chemistry. Further, a compilation of all previously published geochemical data on ophiolites (of all known ages) will be produced and made available to the scientific community. This research represents a critical step forward from the current state of limited data for Proterozoic ophiolites and a fragmentary data archive of ophiolite chemistry. 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.