Geochemistry of intermediate olivine‐phyric shergottite Northwest Africa 6234, with similarities to basaltic shergottite Northwest Africa 480 and olivine‐phyric shergottite Northwest Africa 2990 |
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| Authors: | Justin FILIBERTO Emily CHIN James M D DAY Ian A FRANCHI Richard C GREENWOOD Juliane GROSS Sarah C PENNISTON‐DORLAND Susanne P SCHWENZER Allan H TREIMAN |
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| Institution: | 1. Department of Geology, Southern Illinois University Carbondale, 1259 Lincoln Road, Mailcode 4324, Carbondale, Illinois 62901, USA;2. Department of Earth Science, Rice University, 6100 Main Street, Houston, Texas 77005, USA;3. Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, California 92093–0244, USA;4. Planetary and Space Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK;5. Lunar and Planetary Institute, USRA, 3600 Bay Area Blvd, Houston, Texas 77058, USA;6. Present address: American Museum of Natural History, New York, New York 10024, USA;7. Department of Geology, University of Maryland, College Park, Maryland 20742, USA;8. CEPSAR, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK |
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| Abstract: | Abstract— The newly found meteorite Northwest Africa 6234 (NWA 6234) is an olivine (ol)‐phyric shergottite that is thought, based on texture and mineralogy, to be paired with Martian shergottite meteorites NWA 2990, 5960, and 6710. We report bulk‐rock major‐ and trace‐element abundances (including Li), abundances of highly siderophile elements, Re‐Os isotope systematics, oxygen isotope ratios, and the lithium isotope ratio for NWA 6234. NWA 6234 is classified as a Martian shergottite, based on its oxygen isotope ratios, bulk composition, and bulk element abundance ratios, Fe/Mn, Al/Ti, and Na/Al. The Li concentration and δ7Li value of NWA 6234 are similar to that of basaltic shergottites Zagami and Shergotty. The rare earth element (REE) pattern for NWA 6234 shows a depletion in the light REE (La‐Nd) compared with the heavy REE (Sm‐Lu), but not as extreme as the known “depleted” shergottites. Thus, NWA 6234 is suggested to belong to a new category of shergottite that is geochemically “intermediate” in incompatible elements. The only other basaltic or ol‐phyric shergottite with a similar “intermediate” character is the basaltic shergottite NWA 480. Rhenium‐osmium isotope systematics are consistent with this intermediate character, assuming a crystallization age of 180 Ma. We conclude that NWA 6234 represents an intermediate compositional group between enriched and depleted shergottites and offers new insights into the nature of mantle differentiation and mixing among mantle reservoirs in Mars. |
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