3 Quaternary Volcanoes and Widespread Tephras of the World Hiroshi MACHIDA Professor emeritus, Tokyo Metropolitan University
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[email protected] Abstract It is the two contrasting volcanic products, flood basalt and silicic ignimbrite, that represent the largest known volcanism in the earth history. The former is a product of effusive eruption at hot spots and divergent plate margins, forming extensive lava plains and shield volcanoes. On the other hand the ignimbrite is usually associated with large calderas on the conversion boundary and continental rift, forming ignimbrite sheets and co-ignimbrite volcanic tephras. Many extraordinarily large tephras have been recognized not only on land but also from abyssal sediments. This paper particularly focuses on the significance of Quaternary widespread tephras. A catalogue of the large volume tephras of the Quaternary around the world is tentatively listed, because they are very powerful tools for correlating stratigraphic sequences and landforms extensively, particularly for land-sea correlation. Continual revision and supplement action for compilation of the tephra catalogue will be a task for future studies. Key words: co-ignimbrite ash, flood basalt, ignimbrite, plate tectonics, Quaternary, tephra catalogue, widespread tephra 1. Volcanoes of the World the Pacific, Indian and Atlantic Oceans. Examples include the Hawaiian islands, the Maldive Islands and The theory of plate tectonics is a well supported others. Volcanic islands of this type are chielfly model and one which is able to describe the distri- composed of basaltic lavas with small volumes of bution of volcanoes of different types on the surface silica-rich materials. They form large shield volca- of the earth.