The Petrology of Abyssal Serpentinites: New Insights from Phase Petrology and Geochemical Reaction Path Modeling

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

The reaction of seawater with exposed ultramafic mantle and lower crustal rocks at slow and ultra-slow spreading mid-ocean ridges (a process called serpentinization) has important implications for the chemistry of the oceans, as well as the mechanical and magnetic properties of the seafloor. Unraveling the geochemical consequences of these reactions is key to furthering our understanding of global geochemical cycles, particularly of water and carbon dioxide. Serpentinization is associated with strongly reducing conditions that lead to the generation of free hydrogen gas, and fluids with a low pH; and the Hydrogen and methane released during serpentinization support microbial communities that form the base of the food web in unique and complex ecosystems. Despite the importance of the serpentinization process in changing the physical and chemical nature of the oceanic lithosphere, the reaction pathways of serpentinization are poorly understood and much more complicated than previously anticipated. They are chiefly controlled by the temperature of alteration, fluid flux, and initial rock composition, and hence are highly variable. This research involves a comparative analytical and modeling study of the mineralogy and geochemistry of serpentinized peridotites from different deep-sea environments, including mid-ocean ridges, continental rifted margins, and the forearc mantle of subduction zones. A combination of traditional microprobe and cutting edge synchrotron techniques will be used on Ocean Drilling Program drill cores to determine the textural associations and chemical compositions of secondary minerals. Results with be compared with thermodynamic models to gain deeper insights into the formation conditions and reaction pathways during serpentinization. Broader impacts of the work include support of an early career researcher with no prior NSF support and train two undergraduate students from Bridgewater State College in Massachusetts. It also involves use of national lab facilities at the Advanced Light Source at Lawrence Berkeley Lab in California.