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Title: A new approach to cosmogenic corrections in 40Ar/39Ar chronometry: Implications for the ages of Martian meteorites

Journal Article · · Geochimica et Cosmochimica Acta
 [1];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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Anomalously old 40Ar/39Ar ages are commonly obtained from Shergottites and are generally attributed to uncertainties regarding the isotopic composition of the trapped component and/or the presence of excess 40Ar. Old ages can also be obtained if inaccurate corrections for cosmogenic 36Ar are applied. Current methods for making the cosmogenic correction require simplifying assumptions regarding the spatial homogeneity of target elements for cosmogenic production and the distribution of cosmogenic nuclides relative to trapped and reactor-derived Ar isotopes. To mitigate uncertainties arising from these assumptions, a new cosmogenic correction approach utilizing the exposure age determined on an un-irradiated aliquot and step-wise production rate estimates that account for spatial variations in Ca and K is described. Data obtained from NWA 4468 and an unofficial pairing of NWA 2975, which yield anomalously old ages when corrected for cosmogenic 36Ar using conventional techniques, are used to illustrate the efficacy of this new approach. For these samples, anomalous age determinations are rectified solely by the improved cosmogenic correction technique described herein. Ages of 188 ± 17 and 184 ± 17 Ma are obtained for NWA 4468 and NWA 2975, respectively, both of which are indistinguishable from ages obtained by other radioisotopic systems. For other Shergottites that have multiple trapped components, have experienced diffusive loss of Ar, or contain excess Ar, more accurate cosmogenic corrections may aid in the interpretation of anomalous ages. In conclusion, the trapped 40Ar/36Ar ratios inferred from inverse isochron diagrams obtained from NWA 4468 and NWA 2975 are significantly lower than the Martian atmospheric value, and may represent upper mantle or crustal components.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1376028
Alternate ID(s):
OSTI ID: 1328522
Report Number(s):
LLNL-JRNL-679018; PII: S0016703716302149
Journal Information:
Geochimica et Cosmochimica Acta, Vol. 187, Issue C; ISSN 0016-7037
Publisher:
The Geochemical Society; The Meteoritical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 9 works
Citation information provided by
Web of Science

References (32)

Argon-39-argon-40 “ages” and trapped argon in Martian shergottites, Chassigny, and Allan Hills 84001 journal May 1999
39 Ar- 40 Ar dating of the Zagami Martian shergottite and implications for magma origin of excess 40 Ar journal July 2008
39 Ar- 40 Ar “ages” and origin of excess 40 Ar in Martian shergottites journal June 2009
A petrogenetic model for the origin and compositional variation of the martian basaltic meteorites journal December 2003
40Ar/39Ar study of plagioclases from the Rogaland anorthosite complex (SW Norway); an attempt to understand argon ages in plutonic plagioclase journal July 2001
Argon diffusion in plagioclase and implications for thermochronometry: A case study from the Bushveld Complex, South Africa journal November 2009
Excess argon in melt inclusions in zero-age anorthoclase feldspar from Mt. Erebus, Antarctica, as revealed by the method journal September 1997
Common asteroid break-up events of eucrites, diogenites, and howardites and cosmic-ray production rates for noble gases in achondrites journal January 1995
Ion microprobe measurements of 18O/16O ratios of phosphate minerals in the Martian meteorites ALH84001 and Los Angeles journal June 2003
Excess40Ar in metamorphic rocks from Broken Hill, New South Wales: implications for40Ar/39Ar age spectra and the thermal history of the region journal September 1981
Age calibration of the Fish Canyon sanidine 40Ar/39Ar dating standard using primary K–Ar standards journal January 2007
Shergottites Dhofar 019, SaU 005, Shergotty, and Zagami: 40 Ar- 39 Ar chronology and trapped Martian atmospheric and interior argon journal February 2009
Identification of excess 40Ar by the 40Ar/39Ar age spectrum technique journal October 1976
A Younger Age for ALH84001 and Its Geochemical Link to Shergottite Sources in Mars journal April 2010
A redetermination of the isotopic abundances of atmospheric Ar journal September 2006
Solar and cosmogenic argon in dated lunar impact spherules journal March 2007
Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover journal July 2013
Ar–Ar ages and trapped Ar components in Martian shergottites RBT 04262 and LAR 06319 journal November 2013
Issues in dating young rocks from another planet: Martian shergottites journal June 2013
Application of deuteron–deuteron (D–D) fusion neutrons to 40Ar/39Ar geochronology journal January 2005
Response to the comment by W.H. Schwarz et al. on “Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology” by P.R. Renne et al. (2010) journal September 2011
Chemical characteristics of the lherzolitic shergottite Yamato 000097: magmatism on Mars inferred from the chemical compositions of shergottites journal September 2009
Paleotemperatures at the lunar surfaces from open system behavior of cosmogenic 38Ar and radiogenic 40Ar journal April 2015
Martian Noble Gases journal January 2002
The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites journal March 2008
A MATLAB™ code to perform weighted linear regression with (correlated or uncorrelated) errors in bivariate data journal April 2011
ArAr chronology of the Martian meteorite ALH84001: Evidence for the timing of the early bombardment of Mars journal September 1997
Noble gases and cosmogenic radionuclides in the Gold Basin L4 chondrite shower: Thermal history, exposure history, and pre-atmospheric size journal January 2003
Cosmic-Ray-Produced Noble Gases in Meteorites journal January 2002
Noble gases in 18 Martian meteorites and angrite Northwest Africa 7812-Exposure ages, trapped gases, and a re-evaluation of the evidence for solar cosmic ray-produced neon in shergottites and other achondrites journal January 2016
The case for a martian origin of the shergottites, II. Trapped and indigenous gas components in EETA 79001 glass journal March 1986
Unified equations for the slope, intercept, and standard errors of the best straight line journal March 2004

Cited By (3)

Geochronology of an Apollo 16 Clast Provides Evidence for a Basin‐Forming Impact 4.3 Billion Years Ago journal October 2019
Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy journal May 2018
Interpreting and reporting 40Ar/39Ar geochronologic data journal July 2020

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Related Subjects

58 GEOSCIENCES
79 ASTRONOMY AND ASTROPHYSICS
Mars
Shergottite
40Ar/39Ar
Chronology
Cosmogenic