October 2007 - April 2009DOEI began supporting Zhengrong Wang as a Postdoctoral Scholar in the autumn of 2005. A summary of his educational experiences and his current research work is detailed below.
My hometown is named Lanzhou (also known as Lanchow), a city in central China on the banks of the Yellow River north of Chengdu and south of Mongolia. I fell in love with geological sciences when I was very young, partly due to the mountains and strange-looking rocks carved by Yellow River, and partly due to my specifically chosen name, Zhengrong, given to me by my father. My name is formed by two Chinese characters, both of which are related to mountains. After graduation from high school, I studied geochemistry at the Earth, Atmosphere and Planetary Science Department at the University of Science and Technology of China. In 1999, I started my Ph.D studies at the California Institute of Technology working with Prof. John Eiler on oxygen isotope geochemistry of Hawaiian volcanic rocks. I joined WHOI as a DOEI postdoctoral scholar in late 2005.During 12 years of my studies in geochemistry, I was trained as an isotope geochemist using isotopes to trace and date reservoirs and processes of geological interests. Since then, I have focused on a few research projects described below.
Surveys of Mg isotope variation on naturally occurred materials
Mg (24Mg, 25Mg and 26Mg) is one of the most important rock-forming elements, playing important roles in the ocean, hydrological and biological systems. Its stable isotopes can be used to constrain the processes responsible for their natural distributions. Working closely with Stan Hart, Jerzy Blusztajn, Larry Ball, and Dave Schneider, I am developing techniques and procedures for the precise determination of Mg isotope composition of naturally-occurring Mg-bearing materials using the Neptune facility (Inductively-Coupled-Plasma Multi-collector Mass-spectrometry). These include minerals from typical upper mantle rock (e.g. garnet, olivine, clinopyroxene and orthopyroxene), carbonate, hydrothermal minerals and fluid, seawater and river water. Currently, we are able to routinely measure Mg isotope composition in silicates, carbonates and fluid with good precision. Using this technique, I am working with Anne L. Cohen, Glenn Gaetani, Rinat Gabitov, and Stan Hart to understand Mg isotope fractionation during biomineralization of carbonate. Our studies show that Mg isotope fractionation between coral and seawater could be used as a promising paleothermometer having advantages over other paleoproxies in that it is hardly affected by non-equilibrium isotope fractionation involving biological process. I am also working with Jeff Seewald, Bernhard Peucker-Ehrenbrink and Stan Hart on studying Mg isotope fractionation between hydrothermal fluid and minerals.
Trace element partitioning between siliceous melt and upper mantle minerals
Geochemically, siliceous melt (SiO2-rich melt, e.g. eclogite melt) is thought to contribute significantly to the formation of ocean island basalts. However, Si melts are very reactive, and lose their original geochemical signatures after intense interaction between the melt and upper mantle rocks. In additional to isotope fractionations, trace element partitioning between various phases during this reaction is also dictated by thermodynamics. Understanding this partitioning as a function of temperature, pressure and melt compositions in the controlled lab experiments could provide a framework for revealing the conditions and processes under which these reactions happen. This information is crucial to retrieving eclogite signatures and recognizing melt transport processes, thereby helping to constrain the source, scale and extent of geochemical heterogeneities in the mantle. In this second project, I am closely working with Glenn Gaetani, Nobu Shimizu and Stan Hart. We are currently conducting an experiment studying the interactions between eclogite melt and olivines using trace element partitioning and isotope fractionations. Several recent experiments have been carried out to investigate the melting behavior of MORB (Mid-Ocean Ridge Basalts)-like eclogite and pyroxenite. Our preliminary results show that Ni concentration in olivines could be used as an indicator for the presence of eclogite melt.