EAGER: Recycled Carbonate-Rich Sediment in the Hawaiian Plume? Evidence from Ca Isotopes

Harvard University, Cambridge MA

Investigators

Abstract

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5) The proposed EaGER (Early Grant for Exploratory Research) is designed to facilitate the application of a new geochemical tool (Ca isotopes) to the field of mantle geochemistry using the well-studied Hawaiian lavas as a case study. This is an exploratory study that is still in its early stages of development and, hopefully, will demonstrate through further work that Ca isotopes can be used as a reliable test of recycled sediments in mantle sources. This proposal involves two early career scientists (Huang and Farkas) at Harvard University who will combine their expertise in different fields, and will educate and train graduate and undergraduate students in state-of-the-art analytical techniques and their applications to geosciences. The proposed research will also leverage previous NSF investments by using samples recovered from Hawaii Scientific Drilling Project and Koolau Scientific Drilling Project that were funded via NSF programs. As the fifth most abundant element on the Earth, Ca is a major constituent of three out of the four major minerals present in the Earth's mantle, and it plays an important role in our understanding of mantle melting and mantle convection. Recent development in Ca isotopic analysis revealed large isotopic variations in modern and ancient carbonates, with ancient carbonates having significantly lighter Ca isotopic ratios (lower 44Ca/40Ca) than modern mantle values. Recycling of ancient carbonates into the mantle can, therefore, introduce Ca isotopic variations in mantle-derived lavas. Hawaiian volcanoes are one of the best examples of mantle plume-derived volcanism, and extensive geochemical and isotopic studies on Hawaiian lavas indicate that recycled ancient oceanic crust and sediments are important in the petrogenesis of Hawaiian lavas. The ultimate purpose of this EaGER is to expand preliminary analyses that have shown a slightly lower 44Ca/40Ca than typical mantle 44Ca/40Ca value for some Hawaiian lavas that could be due to the incorporation of recycled carbonate sediments. If fully successful, the results will have great impact on our current understanding of mantle convection and global carbonate cycles, as well as the behavior of Ca isotopes during magmatic processes.