One possible location with the right criteria is the San Francisco Volcanic Field in Northern Arizona. This volcanic field is one of the most diverse and complex eruptive centers in North America. Volcanic features in the field include maars and tuff rings, numerous monogenetic scoria cones and lava flows, and six major intermediate to silicic volcanic centers comprising domes and a stratovolcano. The scoria cones have erupted along two main fault-controlled alignments north-south and northeast-southwest. A few of these scoria cones produced a final dacite or rhyolite dome in the center of the cone. The silicic centers are concentrated on a different northeast-southwest line, thought to represent buried Paleozoic fault traces (Valentine et al., 2021). Lava types erupted from over 600 vents range in composition from picro-basalt to trachyte, and rhyolite along a generally calc-alkalic trend. Some of the lavas have the distinctive elemental ratios that are generally considered indicative of subduction zone magma even though the volcanic field is far away from any recently active subduction zones. The magma sources are diverse, including mafic asthenospheric melts as well as lower crust derived melts. Magma diversity has been effected by variable crustal melting of garnet-bearing upper mantle, mixing between different mantle source domains, extreme crystal fractionation, mixing of rhyolite and mafic melts, crustal anatexis, and assimilation (Arculus and Gust, 1995). San Francisco Mountain (“the Peaks”, figure 9) is the most prominent volcano in northern Arizona, its summit being the highest point in the state. It is located at the junction of three of the major fault alignments that provide structural control for the volcanic field. The present mountain peaks are remnants of two original stratocones which underwent sector collapse towards the northwest, leaving behind a substantial debris fan and an interior valley known as the Inner Basin. Numerous intermediate to silicic flows, dikes, and domes comprise the structure of San Francisco Mountain, and many of these at different structural depths are exposed in the inner basin. This provides strong stratigraphic control for these flows. Several satellite volcanoes are near to San Francisco Mountain and have flows that overlap. Additionally, numerous radiometric dates have been obtained for many of these individual flows. Figure 10 shows dates referenced by Holm (2021) plotted against the stratigraphic position of the relevant flows. In general, the more recent Ar-Ar dates do not agree with the K-Ar ages, either up or down. Due to the large uncertainties, it is possible to select a consistent sequence of dates that would agree with the stratigraphic ordering. The most likely ages, however, have inconsistencies where a younger flow dates older. Additionally, dacite dates may be on the whole older than the other lithology types. The Ar-Ar results are also strikingly different, seeming to indicate much less time between eruptive phases than the equivalent K-Ar ages. The size of the measurement uncertainties prevents making conclusions at this time, but this locality should be investigated with more high-quality radiometric measurements using multiple methodologies. Samples should be taken from all volcanic rocks exposed on San Francisco Mountain, Mount Elden, and the Dry Lake Hills that are able to be fit into the regional stratigraphy. Additionally, samples of basalt and dacite should be taken from the monogenetic cones which erupted both types (Strawberry and O’Neill craters). High quality radiometric analyses should be done on all of these samples including Ar-Ar and U-Pb methods. These would be evaluated against the stratigraphy for out-of-order dating based on composition. Out-of-order dating has occasionally been observed in other settings and has been explained by various mechanisms including Ar loss through recoil effects (Baksi, 1994). Studies like these should also be evaluated in depth. V. CONCLUSION The 2005 RATE study fundamentally changed the way that radiometric dates should be interpreted by showing conclusive evidence for at Figure 9. San Francisco Mountain (“The Peaks”) in Northern Arizona is a complex stratovolcano with lava types ranging from basalt to trachyte, andesite, dacite, and rhyolite, many of which overlap in stratigraphically discernible relationships. H - Humphreys Peak, A - Agassiz Peak, F - Fremont Peak, D - Doyle Peak, S - Schultz Peak. The lake bed and hills in the foreground are a tuff ring known as Dry Lake. MOGK Disequilibrium Relaxation Following Accelerated Nuclear Decay 2023 ICC 340
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