伊豆・小笠原弧北部の火山岩量

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Amounts ofvo1canic materials along northern Izu-Bonin Arc were calculated based on the topographic maps (Latitude 30°40' N to 35°00' N) for the first time. The method of the volume calculation is as follows; First, all of the seamounts and knolls are picked up from the topographic maps with careful examination by using topographic cross sections as well as seismic profiles across them as for the submarine area. Subaerial volcanoes were treated by using topographic maps as well as topographic cross sections of them. We regarded individual volcanoes as a come or elliptical cone, then calculated their volumes and summed them up. The characteristic features of the volume are as follows. (1) Volume of volcanic matedal across northern Izu-Bonin Arc has maximum just on the volcanic front but it decreases toward backarc side. This feature is quite similar to that of Northeast Japan or other arcs. However, the volume of volcanic material increases again Nishi shichito Ridge (backarc echelon ridges), which have large seamoumts with comparable size to volcanoes on the volcanic front. These seamounts are thought to be Tertiary volcanoes. (2) The volume of volcanic material along the volcanic front increases northward from near Aogashima. This pattermn is concordant with existence of thick continental crusts surrounded by 1000 m depth of contour line. This suggests that the volume of volcanic material on the volcanic front has close relationship to the growth of the arc. (3) On the volcanic front, edifice of large basaltic stratovolcano is clearly different from that of an acidic submarine volcano or caldera. The former is three or four times as large as the latter. (4) Volume of volcanoes on the volcaic front of Izu-Bonin Arc is larger than those on the backarc region except volcanoes on the Nishi shichito Ridge. Volume of volcanic material along the arc shows minimum values at some places, where spacing of volcanoes along the volcanic front of the Arc are much wider compared to the other place. These results concern the volume of volcanic material offer prime role of understanding how island arcs develop and what is the essential factor to constract them.
特定非営利活動法人日本火山学会の論文
1990-12-28

伊豆・小笠原弧北部の火山岩量

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