DOI: 10.1016/j.epsl.2018.06.024
Scopus记录号: 2-s2.0-85049344663
论文题名: An evidence-based approach to accurate interpretation of 40Ar/39Ar ages from basaltic rocks
作者: Heath M. ; Phillips D. ; Matchan E.L.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2018
卷: 498 起始页码: 65
结束页码: 76
语种: 英语
英文关键词: 40Ar/39Ar dating
; basalt
; fractionation
; geochronology
; inverse isochron
; recoil
Scopus关键词: Fractionation
; Geochronology
; Heating
; Isotopes
; Mass spectrometry
; Analytical precision
; High temperature heating
; Intermediate temperatures
; inverse isochron
; Negative correlation
; recoil
; Sample preparation procedure
; ^40Ar/^39Ar dating
; Basalt
英文摘要: Since its inception in the mid-1960s, the 40Ar/39Ar dating technique has been the premier method for determining the eruption ages of basaltic rocks, providing valuable insights into a plethora of terrestrial and planetary processes. Advances in multi-collector mass spectrometry and improved sample preparation procedures are enabling ever-improving analytical precision and clearer evaluation of the isotopic disturbances that affect many basaltic samples and cause discordant 40Ar/39Ar age spectra. Here, we present 40Ar/39Ar step-heating data for multiple samples from two Quaternary basalt flows (0.8038 ± 0.0017 and 2.309 ± 0.009 Ma) of the intraplate Newer Volcanic Province, southeast Australia. A small proportion of these samples give concordant 40Ar/39Ar results, but most are variably discordant. The factors controlling these disturbances and implications for accurate age determination are examined and modelled in both step-heating spectra and inverse isochron space. We demonstrate that the proportion of radiogenic 40Ar (40Ar⁎) present in these samples strongly influences the nature of the discordance reflected in 40Ar/39Ar data. Mass-dependent fractionation appears to have a major influence on low-40Ar⁎ samples, whereas 39Ar recoil loss/redistribution effects are evident in samples with higher 40Ar⁎ proportions. The impact of mass fractionation is quantified via step-heating analyses of unirradiated basalt, whereby a ∼4% difference in 38Ar/36Ar ratios is observed between low- and high-temperature heating steps. On an inverse isochron plot (39Ar/40Ar vs 36Ar/40Ar), isotopic disturbance for groundmass samples primarily manifests as isochron rotation, leading to a negative correlation between initial 40Ar/36Ar ([40Ar/36Ar]i) values and associated 40Ar/39Ar ages. We propose a new framework for the interpretation of 40Ar/39Ar step-heating data for basaltic samples, through judicious evaluation of inverse isochron data, (40Ar/36Ar)i ratios and inverse isochron ages. Results from this study suggest that only samples exhibiting both flat 40Ar/39Ar age spectra and atmospheric (40Ar/36Ar)i ratios yield accurate eruption ages; in the case of more discordant age spectra, intermediate temperature steps with atmospheric (40Ar/36Ar)i ratios may provide the closest approximation of the eruption age. © 2018 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/109754
Appears in Collections: 影响、适应和脆弱性 气候变化事实与影响
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作者单位: School of Earth Sciences, The University of Melbourne, VIC, Parkville, 3010, Australia
Recommended Citation:
Heath M.,Phillips D.,Matchan E.L.. An evidence-based approach to accurate interpretation of 40Ar/39Ar ages from basaltic rocks[J]. Earth and Planetary Science Letters,2018-01-01,498