A comparative study of different radiometric dating techniques applied to Quaternary volcanic rocks from Jeju Island, South Korea

Abstract

To constrain the timing of magma emplacement and eruption of volcanic rocks at Mt. Halla, Jeju Island, South Korea, a range of dating techniques (U-Pb, U-Th disequilibrium, and (U-Th)/He dating of zircon, and ⁴⁰Ar/³⁹Ar dating of groundmass) were applied to one trachyandesite sample and one trachyte sample. Trachyandesite sample CS92-7 from north of Mt. Halla yielded a homogeneous population of zircon U-Pb crystallization ages averaging 97 ± 3 ka and U-Th disequilibrium ages averaging 96.2 + 6.2/−10.6 ka. Both groundmass ⁴⁰Ar/³⁹Ar ages and zircon (U-Th)/He ages corrected for disequilibrium record the time of sample cooling, yielding ages of 105 ± 5 ka and 105.4 ± 4.0 ka, respectively. The nearly concordant crystallization and cooling ages are interpreted to document eruption of the sample shortly after its relatively rapid crystallization in the magma reservoir. The eruption age of this sample, based on the available geo- and thermochronological results, is estimated at 100.4 ± 7.6 ka. Trachyte sample SS35-23 from south of Mt. Halla yielded an overdispersed spectrum of zircon crystallization ages, suggesting protracted crystallization in the magma reservoir over a period of at least 140 ka. Weighted mean ages of 40.0 ± 5.9 ka and 39.4 ± 3.8 ka (determined from U-Pb and U-Th disequilibrium dating of the youngest coherent subpopulation, respectively), provide a maximum limit for the eruption age. The eruption age is directly constrained in this work at 32.4 ± 8.4 ka by (U-Th)/He data. The ⁴⁰Ar/³⁹Ar age of 54 ± 7 ka is distinctly different from the zircon crystallization and eruption ages, and is considered to be inaccurate due to a possible issue with sample contamination or excess argon. The combined geochronological methods applied in this study constrain the timing of zircon crystallization, magma residence, and eruption of volcanic rocks on Jeju Island, and provide essential information further improving our understanding of the chronological history of volcanic rocks on Jeju Island.