12:00 PM - 12:15 PM
[SCG64-12] Reconstruction of zircon U–series dating for investigation of high-temperature magma process
Keywords:Zircon, U-series dating, Magma process
After deforming the formula in Wendt and Carl (1985), which represents relationship among the numbers of atoms in 238U- decay series, we have introduced a new equation associated with zircon crystallization age, which including information about 232Th- decay series and common Pb. In equation 1, the 't' denotes zircon crystallization age, and 'c' and 'm' represent common Pb and measured isotopic ratios, respectively. This indicates that accurate crystallization age can be derived by measuring isotopic ratios in equation 1 without depending on uncertain estimation of Th/U and Pa/U partitioning in zircon–melt system.
We also provide analytical technique for this method using laser ablation-ICP tandem quadrupole mass spectrometry (LA-ICP-MS/MS). To measure 230Th/238U in zircon accurately by LA-ICP-MS, great care must be taken for abundance sensitivity and polyatomic interferences due to the existence of tailing from 232Th mass peak and Zr2O3+ (Guillong et al., 2015). With the present LA-ICP-MS/MS technique, high abundance sensitivity of better than <0.3 ppb can be achieved, and thus the possible interferences from polyatomic ions can be successfully removed. Several reference zircon samples were used to evaluate the reliability of the measurement of 230Th/238U and other isotopic ratios in equation 1. The resulting values showed good agreement with the reference values. In this presentation, we would like to demonstrate first application of new dating method to Quaternary zircon samples, and discuss its effectiveness for magma process study.
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