Multiple volcanic eruption episodes in the highlands of Mt. Halla (Hallasan), Jeju Island, Korea: 40Ar/39Ar ages of lava flows

We present 40Ar/39Ar age of 20 volcanic rocks from National Park of Mt. Halla (Hallasan) in an attempt to understand the volcanism of highlands of volcano. We report reliable absolute ages of whole rock (groundmass) and feldspar phenocrsts based on concordant plateau and isochron ages by incremental heating 40Ar/39Ar method. The volcanism of the highlands of Mt. Halla has lasted for approximately 170,000 years and is divided into two major volcanic episodes, 0.182 similar to 0.100 Ma and 0.095 similar to 0.014 Ma. Although we failed to get the whole rock age from Baengrokdam trachyte due to severe weathering, 50.1 +/- 6.2 ka (total fusion age) from anorthoclase phenocrysts is reported. The youngest ages, 17.7 +/- 2.7 ka and 16.2 +/- 3.9 ka from the topmost lava flow with basaltic trachyandesite composition covering the eastern part of Baengrokdam imply that the last episode of lava effusion from the summit crater may have occurred between ca. 20 ka and ca. 14 ka. In the future, the existing volcano stratigraphy of Mt. Halla should be revised and additional research including deep drilling should be performed to understand the volcanism of Mt. Halla in detail.