Paper No. 2
Presentation Time: 8:20 AM


CARTWRIGHT, Julia A.1, FARLEY, Kenneth A.2, HUROWITZ, Joel A.3, ASIMOW, Paul D.1 and JACOBSON, Nathan S.4, (1)Division of Geological and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, (2)Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, (3)Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA, Stony Brook, NY 11794, (4)Glenn Research Center, NASA, 21000 Brookpark Road, Cleveland, OH 44135,

Measuring absolute ages of planetary surfaces is vital for understanding the geological evolution of planetary bodies. Unlike the lunar surface, which has been dated using a combination of absolute dating of returned samples and crater counting techniques, the Martian surface lacks absolute age markers: we have neither returned samples nor in-situ age determinations. Instead, we must rely on crater counting techniques and a Mars/Moon cratering ratio, which likely cause significant uncertainties in absolute age estimates.

Here, we discuss our novel K-Ar dating technique – ID-KArD (Isotope Dilution K-Ar Dating) – intended for in-situ dating on the Martian surface. Importantly, this technique eliminates two factors that have previously hindered such age determinations on Mars. Firstly, high fusion temperatures are not required due to the use of a lithium-borate flux agent, which lowers the required sample melting temperature. Secondly, the need for sample mass measurement can be eliminated, through the addition of an isotope dilution double-spike glass. The spike glass has a known 39Ar/41K ratio, which permits K-Ar age determination using only isotope ratios.

For the first proof of concept phase, we selected a well-dated basalt from the Viluy traps (E. Siberia) for analysis, with a K-Ar age of 354.3 ± 3.5 Ma (Courtillot et al., 2010), and a K2O concentration of ~ 0.7 wt%. Combining a single Viluy aliquot with spike glass and lithium borate flux, Ar and K isotope ratios were measured on an MAP 215:50 (Caltech), and by KEMS (GRC), respectively. Our results yielded an age of 351 ± 19 Ma (Farley et al., 2013), in good agreement with the previously published ages.

For the second phase, we have designed and constructed a single instrument for Ar and K analysis of a single sample using mainly off-the-shelf components. Specifically, our instrument includes two ion sources for separate ionisation of Ar (electron impact) and K (thermal), and a quadrupole mass spectrometer. Multiple lenses focus the ion beam towards the detector, and the instrument can run in both Faraday and Multiplier modes. Thus far, we have successfully measured both isotopic systems, and after further testing, we plan to date suitable planetary surface analogues (including terrestrial basalts, impact suites and meteorite material) in the coming weeks.