Paul A. Giesting^1,†, Susanne P. Schwenzer², Justin Filiberto¹, Natalie A. Starkey², Ian A. Franchi², Allan H. Treiman³, Andy G. Tindle⁴ and Monica M. Grady²

¹Department of Geology, Southern Illinois University Carbondale, Carbondale, Illinois, USA
²Department of Physical Science, Planetary and Space Sciences, The Open University, Milton Keynes, UK
³Lunar and Planetary Science Institute, Houston, Texas, USA
⁴Department of Earth Sciences, The Open University, Milton Keynes, UK
^†Department of Geography and Geology, Illinois State University, Illinois, USA

Amphibole in chassignite melt inclusions provides valuable information about the volatile content of the original interstitial magma, but also shock and postshock processes. We have analyzed amphibole and other phases from NWA 2737 melt inclusions, and we evaluate these data along with published values to constrain the crystallization Cl and H2O content of phases in chassignite melt inclusions and the effects of shock on these amphibole grains. Using a model for the Cl/OH exchange between amphibole and melt, we estimate primary crystallization OH contents of chassignite amphiboles. SIMS analysis shows that amphibole from NWA 2737 currently has 0.15 wt% H2O. It has lost ~0.6 wt% H2O from an initial 0.7–0.8 wt% H2O due to intense shock. Chassigny amphibole had on average 0.3–0.4 wt% H2O and suffered little net loss of H2O due to shock. NWA 2737 amphibole has δD ≈ +3700‰; it absorbed Martian atmosphere-derived heavy H in the aftermath of shock. Chassigny amphibole, with δD ≤ +1900‰, incorporated less heavy H. Low H2O/Cl ratios are inferred for the primitive chassignite magma, which had significant effects on melting and crystallization. Volatiles released by the degassing of Martian magma were more Cl-rich than on Earth, resulting in the high Cl content of Martian surface materials.

Reference
Giesting PA, Schwenzer SP, Filiberto J, Starkey NA, Franchi IA, Treiman AH, Tindle AG and Grady MM (2015) Igneous and shock processes affecting chassignite amphibole evaluated using chlorine/water partitioning and hydrogen isotopes. Meteoritics & Planetary Sciences (in Press)
Link to Article [doi:10.1111/maps.12430]

Published by arrangement with John Wiley & Sons