TY - JOUR
T1 - A re-evaluation of the mn-cr systematics of olivine from the angrite meteorite d'orbigny using secondary ion mass spectrometry
AU - McKibbin, Seann J.
AU - Ireland, Trevor R.
AU - Amelin, Yuri
AU - Holden, Peter
AU - Sugiura, Naoji
N1 - Funding Information:
David Clark is acknowledged for help with sample mounting for SHRIMP. David Heslop is thanked for helpful discussion about statistical bias. The Australian National University Centre for Advanced Microscopy provided technical support and access to SEM facilities. Charlotte Allen and Guil Mallmann assisted with the LA-ICP-MS. Gary Huss and two anonymous reviewers are thanked for constructive criticism of the manuscript, and Janne Blichert-Toft for editorial handling. This research was supported by an Australian National University PhD Research Scholarship to SMcK, and grants DP034277 and DP0666751 from the Australian Research Council to TRI and YA.
PY - 2013/12/15
Y1 - 2013/12/15
N2 - 'Quenched' angrite meteorites are among the best time markers of igneous activity in early formed planetesimals of the Solar System. They can be precisely dated by the Mn-Cr extinct nuclide decay system because they contain olivine with high Mn/Cr. Nevertheless, there is disagreement between various determinations of the initial 53Mn/55Mn for this meteorite, hindering their use for cross-calibration between chronometric systems and between Secondary Ion Mass Spectrometry (SIMS) and bulk measurement techniques. Here we re-evaluate the Mn-Cr systematics of olivine from the quenched angrite D'Orbigny using Sensitive High-mass Resolution Ion Micro Probe Reverse Geometry (SHRIMP-RG) to search for heterogeneity in isotope systematics and check for inter-laboratory bias. We investigated possible bias arising due to different data reduction methods and have paid careful attention to the relative sensitivities of Mn and Cr by utilising a three-component mixing model to correct for matrix effects associated with Mg, Fe and Ca zoning in angrite olivine. We have determined an initial 53Mn/55Mn of 3.60 (±0.39)×10-6 and 3.44 (±0.29)×10-6 (2σ errors) for D'Orbigny olivine by the Mean of Ratios and Ratio of Total Counts data reduction methods. These values are in agreement with those found by some previous bulk and mineral-scale determinations, and with the generally accepted initial 53Mn/55Mn of this meteorite, but not with previous SIMS work on this material. The source of this discrepancy remains unclear. We can exclude heterogeneity in D'Orbigny as a source of discrepancy because we used the same sample and the meteorite appears to have consistent initial 53Mn/55Mn over both micro- and macro-scales. The discrepancy between this and the previous SIMS study probably reflects an unrecognised systematic analytical bias, possibly associated with relative sensitivities of Mn and Cr or with mass spectrometric backgrounds (isobaric interferences or scattered ions) which may become significant at very low Cr count rates.
AB - 'Quenched' angrite meteorites are among the best time markers of igneous activity in early formed planetesimals of the Solar System. They can be precisely dated by the Mn-Cr extinct nuclide decay system because they contain olivine with high Mn/Cr. Nevertheless, there is disagreement between various determinations of the initial 53Mn/55Mn for this meteorite, hindering their use for cross-calibration between chronometric systems and between Secondary Ion Mass Spectrometry (SIMS) and bulk measurement techniques. Here we re-evaluate the Mn-Cr systematics of olivine from the quenched angrite D'Orbigny using Sensitive High-mass Resolution Ion Micro Probe Reverse Geometry (SHRIMP-RG) to search for heterogeneity in isotope systematics and check for inter-laboratory bias. We investigated possible bias arising due to different data reduction methods and have paid careful attention to the relative sensitivities of Mn and Cr by utilising a three-component mixing model to correct for matrix effects associated with Mg, Fe and Ca zoning in angrite olivine. We have determined an initial 53Mn/55Mn of 3.60 (±0.39)×10-6 and 3.44 (±0.29)×10-6 (2σ errors) for D'Orbigny olivine by the Mean of Ratios and Ratio of Total Counts data reduction methods. These values are in agreement with those found by some previous bulk and mineral-scale determinations, and with the generally accepted initial 53Mn/55Mn of this meteorite, but not with previous SIMS work on this material. The source of this discrepancy remains unclear. We can exclude heterogeneity in D'Orbigny as a source of discrepancy because we used the same sample and the meteorite appears to have consistent initial 53Mn/55Mn over both micro- and macro-scales. The discrepancy between this and the previous SIMS study probably reflects an unrecognised systematic analytical bias, possibly associated with relative sensitivities of Mn and Cr or with mass spectrometric backgrounds (isobaric interferences or scattered ions) which may become significant at very low Cr count rates.
UR - https://www.scopus.com/pages/publications/84885965678
U2 - 10.1016/j.gca.2013.09.001
DO - 10.1016/j.gca.2013.09.001
M3 - Article
AN - SCOPUS:84885965678
SN - 0016-7037
VL - 123
SP - 181
EP - 194
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -