Meteoritics & Planetary Science 1–19 (2016) doi: 10.1111/maps.12647 The chlorine isotopic composition of Martian meteorites 1: Chlorine isotope composition of Martian mantle and crustal reservoirs and their interactions 1,2* 1,3 1,2 1,3 3,4 J. T. WILLIAMS , C. K. SHEARER , Z. D. SHARP , P. V. BURGER ,F.M.MCCUBBIN , 1,3 1,3 5 A. R. SANTOS , C. B. AGEE , and K. D. MCKEEGAN 1Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA 2Center for Stable Isotopes, University of New Mexico, Albuquerque, New Mexico 87131, USA 3Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87131, USA 4NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, Texas 77058, USA 5Department of Earth, Planetary, and Space Sciences, UCLA, Los Angeles, California 94607, USA *Corresponding author. E-mail:
[email protected] (Received 12 August 2015; revision accepted 01 March 2016) Abstract–The Martian meteorites record a wide diversity of environments, processes, and ages. Much work has been done to decipher potential mantle sources for Martian magmas and their interactions with crustal and surface environments. Chlorine isotopes provide a unique opportunity to assess interactions between Martian mantle-derived magmas and the crust. We have measured the Cl-isotopic composition of 17 samples that span the range of known ages, Martian environments, and mantle reservoirs. The 37Cl of the Martian mantle, as represented by the olivine-phyric shergottites, NWA 2737 (chassignite), and Shergotty (basaltic shergottite), has a low value of approximately À3.8&. This value is lower than that of all other planetary bodies measured thus far.