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Project Progress

Since the last project report we continued the development of noble gas protocols to determine the timing and rates of processes relevant to astrobiology. Experiments were designed and conducted to analyze noble gases trapped in common minerals found in our solar system, including hydrous phases (micas), pyroxene, feldspars, and quartz. We assessed the potential of minerals to record the timing of surface and atmospheric conditions that can be used to characterize past habitable environments (e.g., on early Earth, Mars). Major findings include:

1) Atmospheric Ar and Ne can be trapped in minerals crystallized at mantle depths on Earth (Baldwin and Das, 2013 and submitted). Results indicate that on Earth the atmosphere is recycled to mantle depths in subduction zones (c.f., the deep carbon cycle).

2) The timing of fluid and rock interaction during early stages of Earth’s evolution was further investigated through noble gas experiments on hydrothermal quartz collected from Jack Hills, Australia. These were difficult, time-consuming experiments to perform since quartz generally contains a negligible amount of K, yielding a very low signal for ³⁹Ar for mass spectrometric measurements. Therefore a relatively large quantity of sample material was required for analysis to ensure sufficient argon could be accurately and precisely measured in step heat experiments. Initial results (JHD1C) yielded a saddle-shaped spectrum with minimum ⁴⁰Ar/³⁹Ar ages ranging from 1.40 to 1.63 Ga. The low temperature (300°- 800° C) and highest temperature (1200°-1710°C) steps yielded results that can be interpreted in terms of the release of Cl–rich fluid inclusions. Additional noble gas experiments on Jack Hills quartz samples are in progress.

3) We assessed the potential of low-mass samples, collected by sample return missions to airless planetary objects (e.g., Moon, Mars, asteroids), to reveal planetary surface processes. A manuscript was prepared that reports ⁴⁰Ar/³⁹Ar and cosmic ray exposure ages of plagioclase rich lithic fragments from Apollo 17 regolith. While the ⁴⁰Ar/³⁹Ar ages agreed with previously reported ages for norite samples at this site, variations in cosmic ray exposure ages are interpreted to reflect gardening of the lunar surface. The effects of solar wind implantation were also documented in one sample.