Primordial Krypton in the Terrestrial Mantle Is Not Solar

Introduction: Noble gases are key tracers for the origin of volatiles in the terrestrial planets and of interaction between mantle reservoirs and the atmosphere. General consensus is that material accreting in the solar nebula and nebula gases from the Sun itself were incorporated into the terrestrial planets, providing a starting point for models of planetary evolution. However, the isotopic signatures of these accretion processes are often masked by air contamination and therefore deviations from air may be <1%, requiring high precision measurements. Typically, oceanic basalts, continental diamonds and xenoliths have provided the noble gas data for the mantle. Our current work focuses a suite of samples from individual wells that extract almost pure (>99%) CO2 from beneath New Mexico, USA. These well gases are sourced from deep within the sub-continental lithospheric mantle (SCLM) and have been shown to contain magmatic volatiles retained from the earliest stages of planetary formation [1]. Uniquely, these gases provide essentially unlimited amounts of sample for high precision measurements which, coupled with improved instrument precision from the new generation of noble gas mass spectrometers, allows us to investigate accretionary processes.