STABLE REMANENT MAGNETIZATION FROM PLEISTOCENE LAVA FLOWS IN JEJU GEOPARK

The 7 Wonders of Nature are Amazon, Halong Bay, Iguazu Falls, Jeju Geopark, Komodo, Puerto Princesa Underground River, and Table Mountain by the UNESCO (United Nations Educational, Scientific, and Cultural Organization). We recovered a total of 224 1-inch core specimens from 28 alkaline lava flows of 550 m-thick. Each alkaline lava flow showed a decrease in magnetic grain size from the massive crystalline flow upward into the interiors of rapidly cooled brecciated margin and vesicle streaked zone. In particular, both brecciated margin and vesicle streaked zones contain predominantly fine-grained magnetite as inclusions in feldspars. It is possible that the vesicular fraction is ideally suited for determining faithful paleointensity record as rock magnetic proxies indicate the presence of elongated fine-grained magnetite. It should be also noted that these fine-grained magnetites are encapsuled within plagioclase feldspars. Such silicate armoring of magnetic material is effective in preventing alteration during the multiple heatings necessary for Thellier-type paleointensity determination.