Table 3.

U–Th geochronological analyses from Campo Muri quarry

SampleWeight (g)238U (ppb*)232Th (‰)δ234U measured*[230Th/238U]activity[230Th/232Th] (ppm)Age uncorrected (years)Age corrected (years)†§δ234Uinitial

corrected
NER.C.10.049650.69 ± 0.275887 ± 29214.9 ± 8.10.1226 ± 0.004717.40 ± 0.6711564 ± 4749019 ± 1368220.4 ± 8.4
MUR.C.30.04013.308 ± 0.025249.5 ± 7.2668 ± 310.1269 ± 0.009427.7 ± 2.28583 ± 6827391 ± 899682 ± 32
MUR.C.40.05248.528 ± 0.0541072 ± 10621 ± 170.1527 ± 0.006720.03 ± 0.8910727 ± 5108677 ± 1148636 ± 18
MUR.C.50.054614.83 ± 0.139443 ± 52388 ± 140.349 ± 0.0239.04 ± 0.5831177 ± 232318580 ± 7036409 ± 17

Analytical errors are 2σ of the mean.

*[238U] = [235U] × 137.818 (±0.65‰) δ234U = ([234U/238U]activity − 1) × 1000.

[230Th/238U]activity = 1 − e−λ230T + (δ234Umeasured/1000)[λ230/(λ230 − λ234)](1 − e−(λ230 − λ234)T), where T is the age. Decay constants are 9.1705 × 10−6 a−1 for 230Th, 2.8221 × 10−6 a−1 for 234U (Cheng et al. 2013) and 1.55125 × 10−10 a−1 for 238U (Jaffey et al. 1971).

The degree of detrital 230Th contamination is indicated by the [230Th/232Th] atomic ratio instead of the activity ratio.

§Age corrections, relative to chemistry date of 21 June 2016, for samples were calculated using an estimated atomic 230Th/232Th ratio of 4 ± 2 ppm. These are the values for a material at secular equilibrium, with the crustal 232Th/238U value of 3.8. The errors are arbitrarily assumed to be 50%.

δ234Uinitial corrected was calculated based on 230Th age (T) (i.e. δ234Uinitial = δ234Umeasured × eλ234T) and T is corrected age.