A Tentative Estimation of the Rate of Growth of the "Akashiro" Silica Stone Deposits in Japan

IWAO Shuichi

doi:10.11456/shigenchishitsu1951.26.1

The so-called "Akashiro" silica stone in Japan is a sort of silica rock which is composed of reddish chert fragments and white cementing vein quartz. It has been mined for the domestic use in Japan as a refractive raw material of high quality, for steel industry. It forms thick lenticular and/or massive deposits of various dimensions mostly in the areas of Chichibu geosynclinal terrain of younger Palaeozoic and older Mesozoic eras. The deposits are mostly overlying submarine basalt lave flows and underlie thick bedded cherts of more or less limited horizons in the whole sequence of the formations. The geological occurrences as well as petrographical features of the deposits indicate that they are the products of submarine hydrothermal activities which started subsequent to the outflow of the basalt lavas on the ocean floor, and grew in parallel to the formation of the bedded chert.<BR>Under the most probable assumption, consequently, that the finest clayey fractions of the sediments including both bedded chert and clayslate were accumulated at the same rate throughout the concerned period corresponding to respective known thickness of the sediments in the terrain, the rate of thickning of the bedded chert can be calculated. It gives a time interval of the rhythmus at about n×10² years for the deposition of the single unit bed. Calculating from the thickness of the silica stone deposit and the average thickness-about 4.8 cm-of the single unit bed of the bedded chert, the growing time of the deposits can be estimated at n×10³ - n×10⁴ years, and probably less than n×10⁵ years.

A Tentative Estimation of the Rate of Growth of the "Akashiro" Silica Stone Deposits in Japan

Bibliographic Information

Search this article

Description

Journal

Keywords

Details 詳細情報について

Export

Report a problem