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Discordant K-Ar and Young Exposure Dates for the Windjana sandstone, Kimberley, Gale Crater, Mars

Vasconcelos, P. M. and Farley, K. A. and Malespin, C. A. and Mahaffy, P. and Ming, D. and McLennan, S. M. and Hurowitz, J. A. and Rice, Melissa S. (2016) Discordant K-Ar and Young Exposure Dates for the Windjana sandstone, Kimberley, Gale Crater, Mars. Journal of Geophysical Research. Planets, 121 (10). pp. 2176-2192. ISSN 2169-9097. doi:10.1002/2016JE005017.

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K-Ar and noble gas surface exposure age measurements were carried out on the Windjana sandstone, Kimberley region, Gale Crater, Mars, by using the Sample Analysis at Mars instrument on the Curiosity rover. The sandstone is unusually rich in sanidine, as determined by CheMin X-ray diffraction, contributing to the high K_2O concentration of 3.09 ± 0.20 wt % measured by Alpha-Particle X-ray Spectrometer analysis. A sandstone aliquot heated to ~915°C yielded a K-Ar age of 627 ± 50 Ma. Reheating this aliquot yielded no additional Ar. A second aliquot heated in the same way yielded a much higher K-Ar age of 1710 ± 110 Ma. These data suggest incomplete Ar extraction from a rock with a K-Ar age older than 1710 Ma. Incomplete extraction at ~900°C is not surprising for a rock with a large fraction of K carried by Ar-retentive K-feldspar. Likely, variability in the exact temperature achieved by the sample from run to run, uncertainties in sample mass estimation, and possible mineral fractionation during transport and storage prior to analysis may contribute to these discrepant data. Cosmic ray exposure ages from ^3He and ^(21)Ne in the two aliquots are minimum values given the possibility of incomplete extraction. However, the general similarity between the ^3He (57 ± 49 and 18 ± 32 Ma, mean 30 Ma) and ^(21)Ne (2 ± 32 and 83 ± 24 Ma, mean 54 Ma) exposure ages provides no evidence for underextraction. The implied erosion rate at the Kimberley location is similar to that reported at the nearby Yellowknife Bay outcrop.

Item Type:Article
Related URLs:
URLURL TypeDescription ItemPlanetary Data System
Farley, K. A.0000-0002-7846-7546
Malespin, C. A.0000-0002-5852-5016
Mahaffy, P.0000-0003-1896-1726
Ming, D.0000-0003-0567-8876
McLennan, S. M.0000-0003-4259-7178
Hurowitz, J. A.0000-0002-5857-8652
Rice, Melissa S.0000-0002-8370-4139
Additional Information:© 2016 American Geophysical Union. Received 12 FEB 2016; Accepted 4 OCT 2016; Accepted article online 17 OCT 2016; Published online 27 OCT 2016. Special Section: The Mars Science Laboratory Rover Mission (Curiosity) at The Kimberley, Gale Crater, Mars. The authors thank the Mars Science Laboratory Project teams for an effective and successful mission. Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Data presented in this paper are archived in the Planetary Data System (
Funding AgencyGrant Number
Subject Keywords:Mars; 36Ar; K-Ar; 3He; 21Ne
Issue or Number:10
Record Number:CaltechAUTHORS:20161018-073743780
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Official Citation:Vasconcelos, P. M., K. A. Farley, C. A. Malespin, P. Mahaffy, D. Ming, S. M. McLennan, J. A. Hurowitz, and M. S. Rice (2016), Discordant K-Ar and young exposure dates for the Windjana sandstone, Kimberley, Gale Crater, Mars, J. Geophys. Res. Planets, 121, 2176–2192, doi:10.1002/2016JE005017
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:71199
Deposited By: Tony Diaz
Deposited On:18 Oct 2016 17:40
Last Modified:11 Nov 2021 04:41

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