[2oral601-11] T6 ［トピック］マグマソース・マグマ供給系から火山体形成まで

9:30 〜 9:45

[T6-O-4] Characterization of optimal lava flow textures for ⁴⁰Ar/³⁹Ar and K-Ar dating at Pleistocene volcanoes

*Chris Conway¹, Seiko Yamasaki¹, Osamu Ishizuka¹, Yumiko Harigane¹ (1. Geological Survey of Japan)

キーワード：

Ar/Ar dating、stratovolcanoes、andesite、lava flow、Pleistocene

The ⁴⁰Ar/³⁹Ar and K/Ar geochronometers are valuable tools for defining the eruption histories of Pleistocene arc volcanoes in Japan and around the world. It is particularly important to determine the timing of eruption events over the last 100,000 years to enable assessments of recent trends in magma compositions and volumes at potentially active volcanoes. However, measuring accurate and precise ⁴⁰Ar/³⁹Ar and K-Ar ages for late Pleistocene eruptive products is challenging due to the low yields of radiogenic ⁴⁰Ar in young volcanic rocks.

For this study, we have characterized the textural and compositional features of lava flow groundmass samples for which ⁴⁰Ar/³⁹Ar and K-Ar ages have been determined. Studied samples were collected from Ruapehu volcano in New Zealand, and Chokai, Zao, and Ontake volcanoes in Japan. The sizes and K-contents of groundmass feldspars in these samples were measured and compared with the precision of their age measurements. These datasets have provided preliminary benchmark values for the optimal textures and compositions required for high-precision ⁴⁰Ar/³⁹Ar and K-Ar age measurements of late Pleistocene andesite lava flows.