A review of the present state of the absolute calibration for zircon fission track geochronometry using the external detector method

Danhara, Tohru; Iwano, Hideki

doi:10.1111/iar.12035

Cited by 40 publications

(24 citation statements)

References 78 publications

(134 reference statements)

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“…The ζ-method still appears to be the only accepted option for dating titanite, zircon and minerals more sensitive to irradiation damage than apatite. However, Danhara and Iwano (2013) and Iwano (pers. com., in part based on Iwano and Danhara, 1998) reported standardless fission-track dating of zircon and titanite with the externaldetector method, despite the added complications caused by radiation damage effects.…”

Section: Discussionmentioning

confidence: 99%

Standardless fission-track dating of the Durango apatite age standard

2015

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Five dating strategies were used for determining the standardless fission-track age of the Durango apatite. These use the same fossil-track densities but differ in the manner in which the induced-track densities are determined. A conventional age calculation, without correction for experimental factors, gives inconsistent ages with methodrelated differences N 15%. Correcting for these factors brings the ages in line with each other and with the reference age but leaves no room for a partial-annealing correction based on the confined-track lengths. Three further reasons suggest that a length correction is not appropriate. (1) The evidence for lengthbased corrections is inconclusive. (2) The plateau age of the Durango apatite is consistent with its apparent fission-track age to within 1%. (3) The calculated effective etchable length of the fossil tracks agrees within error with that of the induced tracks; both are further consistent with the measured mean length of confined induced tracks. The circumstance that the (U,Th)/He ages of the accepted and proposed apatite age standards are consistent with their reference ages leaves no margin for a lowered fission-track age resulting from partial annealing, although the case of the Durango apatite itself is inconclusive because of its exceptional crystal size. It is conjectured that the shortening of the fossil tacks in the Durango apatite is due to a lowering of the track etch rate over time. In this case, annealing equations fitted to induced-track data underestimate the extent of confined-track-length reduction in geological samples.

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Section: Discussionmentioning

confidence: 99%

Standardless fission-track dating of the Durango apatite age standard

2015

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“…The Rb–Sr ages (1) are also at variance with the zircon U–Pb ages reported by Usuki et al () and Kemp et al (). Furthermore, the FT ages (3) were obtained by an older method with ζ = ΦσI/λf (ζ, FT age; Φ, the thermal neutron fluence in neutron/cm 2 during irradiation; σ, the cross‐section for thermal‐neutron‐induced 235 U fission; I, isotopic abundance ratio 235 U/ 238 U; λf, spontaneous fission decay constant of 238 U), instead of by the standardized method in which ζ is calculated from age standards (Danhara & Iwano, ).…”

Section: Geology Of the Nakanogawa Group In The Hidaka Beltmentioning

confidence: 99%

U–Pb zircon ages of the Nakanogawa Group in the Hidaka Belt, northern Japan: Implications for its provenance and the protolith of the Hidaka metamorphic rocks

et al. 2017

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Zircon U–Pb ages of two acidic tuff and two turbidite sandstone samples from the Nakanogawa Group, Hidaka Belt, were measured to estimate its depositional age and the development of the Hokkaido Central Belt, northeast Japan. In the northern unit, homogeneous zircons from pelagic acidic tuff from a basal horizon dated to 58–57 Ma, zircons from sandstone from the upper part of the unit dated to 56–54 Ma, and zircons from acidic tuff from the uppermost part dated to 60–56 Ma and 69–63 Ma. Both of the tuff U–Pb ages are significantly older than the youngest radiolarian fossil age (66–48 Ma). Therefore, the maximum depositional age of the turbidite facies in the northern unit is 58 Ma and the younger age limit, estimated from the fossil age, is 48 Ma. In the southern unit, homogeneous zircons from turbidite sandstone dated to 58–57 Ma. Thus the depositional age of this turbidite facies was interpreted to be 66–56 Ma from the fossil age, probably close to 57 Ma. Most of the zircon U–Pb ages from the Nakanogawa Group are younger than 80 Ma, with a major peak at 60 Ma. This result implies that around Hokkaido volcanic activity occurred mainly after 80 Ma. Older zircon ages (120–80 Ma, 180–140 Ma, 340–220 Ma, 1.9 Ga, 2.2 Ga, and 2.7 Ga) give information about the provenance of other rocks in the Hidaka Belt. It is inferred that the Nakanogawa Group comprises protoliths of the upper sequence of the Hidaka Metamorphic Zone, which therefore has the same depositional age as the Nakanogawa Group (66–48 Ma). The depositional ages of the lower sequence of the Hidaka Metamorphic Zone and the Nakanogawa Group are probably the same.

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“…However, the obvious cause for the difference between the measured and calculated transmission profiles is that the experiment compares the etchable track lengths with the calculated ranges of unetched latent 132 Xe and 238 U ion tracks. In materials with high registration thresholds, the distance to the point where the track-forming particle comes to rest exceeds the length over which its track is etchable; this difference is called the range deficit [17][18][19] or length deficit [12,20]. The dashed line (Fig.…”

Section: Discussionmentioning

confidence: 99%