SGER: Development of High-Precision Neodymium Isotope Mass Spectrometry to Search for Crust-Mantle Differentiation on Early Earth

Dartmouth College, Hanover NH

Investigators

Abstract

EAR-0336405 Sharma A major ambiguity remains in ascertaining whether the silicate portion of the Earth underwent differentiation during the first 500 million years of its history-a time for which there is no extant rock record. The evidence of early crust-mantle differentiation event(s) may be present in Archean rocks in the form of 142Nd anomalies produced from the decay of short-lived 146Sm (half-life = 103 million years), which was present at the time of formation of the Earth. The expected level of excess in 142Nd is about +30 parts per million (ppm) and, therefore, a 1-sigma uncertainty of 5 ppm or better is needed to resolve the anomaly. To accomplish this technically challenging task, we will use a new generation thermal ionization mass spectrometer (Triton) recently installed at Dartmouth. Initial measurements of standards on Triton have shown that it is capable of measuring anomalies in 142Nd exceeding +10 ppm. We will develop a standard operating procedure (SOP) to mitigate/eliminate possible ion optical artifacts in order to obtain Nd isotope results that are precise and accurate at 5 ppm (1-sigma) or better. Following the development of the SOP we will examine ten early Archean rocks from Isua, Greenland. Broader impacts of the proposed study include teaching and training of a highly motivated graduated student, Rasmus Andreasen, and development of new techniques of accurate and super-precise measurements of Nd isotopes using thermal ionization mass spectrometry. Also, the study is expected to provide new and profound insights into the history of early Earth differentiation. The unprecedented external reproducibility of Nd-isotope measurements will open up new avenues of investigations in diverse areas of earth and planetary sciences.