Month: September 2016

The effect of titanium on the partitioning behavior of high-field strength elements between silicates, oxides and lunar basaltic melts with applications to the origin of mare basalts

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1Leitzke, F.P., 1Fonseca, R.O.C., 1Michely, L.T., 2Sprung, P., 2Münker, C., 1,3Heuser, A., 1Blanchard, H.
Chemical Geology 440, 219-238 Link to Article [10.1016/j.chemgeo.2016.07.011]
1Steinmann-Institut für Geologie, Mineralogie un Paläontologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
2Institut für Geologie und Mineralogie, Universität zu Köln, Köln, Germany
3GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Wischhofstraße 1-3, Kielz, Germany

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A model for meteoritic and lunar 40Ar/39Ar age spectra: Addressing the conundrum of multi-activation energies

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1P. Boehnke, 1T. Mark Harrison, 2M.T. Heizler, 1P.H. Warren
Earth and Planetary Science Letters (in Press) Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.07.014]
1Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, United States
1New Mexico Bureau of Geology and Mineral Resources, Socorro, NM 87801, United States
Copyright Elsevier

Results of whole-rock 40Ar/39Ar step-heating analyses of extra-terrestrial materials have been used to constrain the timing of impacts in the inner solar system, solidification of the lunar magma ocean, and development of planetary magnetic fields. Despite the importance of understanding these events, the samples we have in hand are non-ideal due to mixed provenance, isotopic disturbances from potentially multiple heating episodes, and laboratory artifacts such as nuclear recoil. Although models to quantitatively assess multi-domain, diffusive 40Ar⁎ loss have long been applied to terrestrial samples, their use on extra-terrestrial materials has been limited. Here we introduce a multi-activation energy, multi-diffusion domain model and apply it to 40Ar/39Ar temperature-cycling, step-heating data for meteoritic and lunar samples. We show that age spectra of extra-terrestrial materials, the Jilin chondrite (K-4) and Apollo 16 lunar breccia (67514,43)(67514,43), yielding seemingly non-ideal behavior commonly interpreted as either laboratory artifacts or localized shock heating of pyroxene, are meaningful and can be understood in context of the presence of multi-diffusion domains containing multiple activation energies. Internally consistent results from both the meteoritic and lunar samples reveal high-temperature/short duration thermal episodes we interpret as due to moderate shock heating.