Analytical data of zircons from tephra in the Oshamambe district（Kuromatsunai lowland）, southwestern Hokkaido

Fig. S1. Outcrop photographs of the sampled tephras. (a)CRGW, (b) CRG_SS, (c) ST-PF. Yellow dashed rectangles (height of rectangles: ~30 cm) denote where samples were collected.

Table S1. Zircon U–Pb dating results. Data marked with #(>75% common Pb contamination) were excluded for further U–Pb analyses.

  

• CRGW (sampling location coordinates: 42.616478,140.316706) measured on 09/30/2020, 10/29/2020
• CRG_SS (sampling location coordinates: 42.607056,140.314058) measured on 09/30/2020
• ST-PF (sampling location coordinates: 42.618414,140.325478) measured on 07/06/2021
• Bishop Tuff (reference age: 0.767±0.001 Ma; Crowley et al., 2007) measured on 09/30/2020, 10/29/2020, 07/06/2021
• Fish Canyon Tuff (reference age: 28.402 ± 0.023 Ma; Schmitz and Bowring, 2001) measured on 09/30/2020, 07/06/2021
• Plešovice (reference age: 337.13±0.37 Ma; Sláma et al., 2008) measured on 09/30/2020, 10/29/2020, 07/06/2021

• a_fTh/U = (Th/U)zircon/(Th/U)magma. (Th/U)magma of 4.0 ± 2.0 for unknown, 3.0 ± 1.5 for Bishop Tuff, and 2.2 ± 1.1 for Fish Canyon Tuff were used.
• b_f₂₀₆% denotes the percentage of ²⁰⁶Pb that is common Pb and is calculated as follows: f₂₀₆% = 100 × (x－0.0461)/(0.832－0.0461), where x is a measured ²⁰⁷Pb/²⁰⁶Pb ratio (Ito et al., 2017).
• c_Measured isotope ratio, that is before corrections of initial ²³⁰Th and ²³¹Pa disequilibrium and common Pb.
• d_Individual U-Pb (²³⁸U-²⁰⁶Pb) ages were determined using the modified ²⁰⁷Pb method (Sakata, 2018). Error of weighted mean is shown as 95% confidence level.
• e_MSWD: mean square weighted deviation.
• f_Statistical outlier identified by applying 2σ criterion in Isoplot (Ludwig, 2012).

References

• Ito, H., Spencer, C.J., Danišík, M., Hoiland, C.W., 2017. Magmatic tempo of Earth’s youngest exposed plutons as revealed by detrital zircon U-Pb geochronology. Scientific Reports, 7: 12457.
• Ludwig K.R., 2012. User’s Manual for Isoplot 3.75: A geochronological toolkit for Microsoft Excel. Berkeley Geochronol. Center Spec. Pub., 5, 75 pp.
• Sakata, S., 2018. A practical method for calculating the U-Pb age of Quaternary zircon: Correction for common Pb and initial disequilibria. Geochem. J., 52, 281–286.

Table S2. Zircon (U–Th)/He analytical results and parameters used for the disequilibrium correction.

TAU - total analytical uncertainty; Raw He age - (U-Th)/He age uncorrected for alpha ejection; Ft - alpha ejection correction factor after Farley et al. (1996); D(230) - parameter describing zircon-melt fractionation of ²³⁰Th/²³⁸U (Farley et al., 2002; Schmitt et al., 2010) calculated as (Th/U)zircon/(Th/U)magma, whereby a value of 4 was used for (Th/U)magma and a value of 3.8 was used as D(231) (Schmitt, 2011); Diseq.-cor. He age - (U-Th)/He age corrected for disequilibrium calculated by using MCHeCalc software (Schmitt et al. 2010). 

References:

• Farley, K.A., Kohn, B.P. and Pillans, B., 2002. The effects of secular disequilibrium on (U–Th)/He systematics and dating of Quaternary volcanic zircon and apatite. Earth Planet. Sci. Lett., 201, 117–125. 
• Farley, K.A., Wolf, R.A. and Silver, L.T., 1996. The effects of long alpha-stopping distances on (U-Th)/He ages. Geochim. Cosmochim. Acta, 60, 4223-4229.
• Schmitt, A.K., 2011. Uranium series accessory crystal dating of magmatic processes. Annu. Rev. Earth Planet. Sci. 39, 321–349.
• Schmitt, A.K., Stockli, D.F., Niedermann, S., Lovera, O.M. and Hausback, B.P., 2010. Eruption ages of Las Tres Vírgenes volcano (Baja California): a tale of two helium isotopes. Quat. Geochronol., 5, 503–511.