the excess daughter products produced during accelerated nuclear decay (AND). Extraneous daughter products, particularly Ar, are a known and well researched topic (see for example Overman, 2013). Technology and knowledge of the behavior of extraneous products has improved since the issue was first encountered, and dates that might once have been discarded are now analyzed to elucidate the crystallization and thermal history of a sample (Kelley, 2002a). Not only isotopes, but entire minerals with their total inventory of radiogenic products can be inherited by a magma (Bea et al., 2021) or metamorphic rock (Sherlock and Kelley, 2002; Giorgis et al., 2000). Much of the excess in the case of argon is known to be concentrated in certain minerals (Harrison et al., 1994; Damon et al., 1967), along grain rims (Lee et al., 1990), and in fluid inclusions (Rama et al., 1965). Techniques, such as in vacuo crushing (Hu et al., 2018) and step heating (Holm-Alwmark et al., 2021), have been developed to distinguish supposedly excess Ar from in situ radiogenic Ar. Given the preferred partitioning of Ar into fluid inclusions and mineral rims, in vacuo crushing allows for the release of the excess without further contaminating the sample with atmospheric argon. The step heating technique for measuring Ar heats the sample slowly in discrete steps which allows Ar in domains near the surface to evolve before that in domains from deeper within the mineral grains. The plateau age is the final age determined from the sample as the most central domains release their Ar. A date may also be obtained from the total amount of gas evolved (Merrihue and Turner, 1966). Laser spot analysis is used on sectioned and polished grains (particularly zircon) to ablate minute amounts of the mineral which is then analyzed for a date. This allows for spatially restricted dating on a fine scale, and mineral rims and cores can be dated separately. Isochron analyses, which can be applied to any radiometric technique, can also be used to determine the initial amount of daughter products incorporated into the mineral. This is accomplished by trading the assumption of zero initial excess for one specifying that deviations between the radiogenic and non-radiogenic daughter isotope is correlated with the parent isotope through the mechanism of nuclear decay. This alternate assumption is susceptible to mixing effects and may also be negatively impacted by loss or addition of parent or daughter. Extreme excess incorporated on fine scales (smaller than the analysis volume) as a result of AND would not be distinguishable from a valid date for all of the methods described above and for any radioisotope system, though it may still contribute to additional, non-cryptic excess. B. HISTORIC LAVA FLOW DATA Snelling (1998) published a list of recent lava flows with known dates from recorded history in which the radiometric ages were greatly inflated. Snelling’s list was not exhaustive and did not include all the measurements reported in the references that he included. Instead, he selected measurements which very clearly demonstrated extraneous argon as an issue in K-Ar and related dating methods. Many of the measurements were done early in the development of K-Ar dating, when the techniques to deal with the known issue of extraneous argon were being developed. Some of these measurements also included the glassy rims of pillow basalts (see for example Fisher, 1972). This rapidly cooled glass more closely represents the composition of the melt as opposed to the crystal fraction of solidifying lava, and so would be expected to have a higher excess. Table 1 is an updated list of selected measurements of historic lava flows. There is significant overlap with Snelling’s references, but the list has been updated to only provide groundmass measurements with some newer additions. This list of historic flows with anomalously high Ar, similarly, is not meant to be exhaustive or normative. Most historic lava flows correctly yield zero radiometric age, but negative measured ages are also possible (Dalrymple, 1969; Krummenacher, 1970). With modern techniques, dating lava flows in the historical realm is feasible Volcano Flow date Age (ka) Reference Mt St Helens 1986 350 ±50 Austin (1996) Mt Erebus 1984 48 ±8 Esser et al. (1997) Mt Erebus 1984 179 ±16 Esser et al. (1997) Mt Erebus 1984 50 ±30 Esser et al. (1997) Mt Erebus 1984 640 ±30 Esser et al. (1997) Mt Erebus 1984 101 ±16 Esser et al. (1997) Mt Ngauruhoe Feb 19 1975 1000 ±200 Snelling (1998) Kilauea 1972 80 ±240 Ozawa et al. (2006) Mt Etna May 1964 700 ±10 Krummenacher (1970) Mt Stromboli Sep 23, 1963 2400 ±2000 Krummenacher (1970) Kilauea Iki 1959 8500 ±6800 Krummenacher (1970) Mt Ngauruhoe Jul 14, 1954 1000 ±200 Snelling (1998) Mt Ngauruhoe Jun 30, 1954 3500 ±200 Snelling (1998) Mt Ngauruhoe Jun 30, 1954 1200 ±200 Snelling (1998) Mt Ngauruhoe Jun 4, 1954 1500 ±100 Snelling (1998) Mt Ngauruhoe Feb 11, 1949 1000 ±200 Snelling (1998) Mt Lassen 1915 110 ±30 Dalrymple (1969) Novarupta 1912 2360 ±50 Shormann (2013) Hualalai 1801 80 ±70 Ozawa et al. (2006) Hualalai 1801 390 ±30 Ozawa et al. (2006) Hualalai 1800–1801 300 ±40 Ozawa et al. (2006) Hualalai 1800–1801 540 ±50 Ozawa et al. (2006) Hualalai 1800–1801 1410 ±80 Dalrymple (1969) Hualalai 1800–1801 1600 ±160 Dalrymple (1969) Hualalai 1800–1801 22800 ±16500 Krummenacher (1970) Kilauea > 1800 12000 ±2000 Noble and Naughton (1968) Kilauea > 1800 21000 ±8000 Noble and Naughton (1968) Mt Etna 1792 350 ±140 Dalrymple (1969) Medicine Lake > 1500 12600 ±4500 Krummenacher (1970) Rangitoto > 1300 150 - 470 McDougall et al. (1969) Sunset Crater 1064–1065 250 ±150 Dalrymple (1969) Sunset Crater 1064–1065 270 ±90 Dalrymple (1969) Kilauea > 1000 42900 ±4200 Dalrymple and Moore (1968) Kilauea > 1000 30300 ±3300 Dalrymple and Moore (1968) Mt Etna 122 BC 250 ±80 Dalrymple (1969) Table 1. Selected published anomalously old K-Ar dates for historic flows. MOGK Disequilibrium Relaxation Following Accelerated Nuclear Decay 2023 ICC 328
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