堆積作用がある場合のプレート生長

―日本海への適用―

抄録

The effects of sedimentation on the thickening process of the lithospheric plate and surface heat flow are examined numerically. For this purpose, we revised the program for the thickening plate model which was used by KONO and YOSHII (1975) to take sedimentation into account.
The results are as follows:
(1) The effect of sedimentation is negligible when the sedimentation rate is smaller than 10^-4cm/yr, which is a typical rate for the ocean basins.
(2) There is, therefore, no need to revise the results of KONO and YOSHII (1975) and YOSHII et al. (1976), which were calculated neglecting sedimentation.
(3) However, when the sedimentation rate is as high as 5×10^-3cm/yr, which is some times realized in the marginal seas and ocean basins near continents, the surface heat flow is decreased considerably.
(4) The sedimentation prevents the thickening of the plate, but this effect is very small compared with the effect on the surface heat flow.
We applied the present model to describe the origin and development of the Japan Sea, a typical example of a maginal sea, to its present state. Two cases were considered for a date of opening of the Japan Basin; the first assume a date of opening of 25 M. Y. B. P. (Miocene) and the second a date of 50 M. Y. B. P. (Palaeogene). The calculations present favorable results for the hypothesis that the Japan Sea opened at about 25 M. Y. B. P. If, however, we take the uncertainty of the parameters used in the present article into consideration, it is difficult to conclude that the opening time of the Japan Sea is in Miocene time only from the present calculations. Therefore, we concluded that whether the opening of the Japan Sea is in Miocene or Palaeogene times, the history of the Japan Sea, based on the thickening plate model, is consistent with the present geophysical and geological observations.