グリーンタフ変動の諸問題

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In the latter half of the 1960's, it was widely recognized that the Green-Tuff movement was one peculiar orogeny which destroyed the structures of the previous orogenic belts, and also was accompanied with the deep-seated fractures causing violent volcanic activities. However, FUJITA, Y. (1967) proposed that the Green-tuff sedimentary basins were formed by the collapsing movements. After his proposition, many investigations into the Green-tuff movement had been made, from tectonic viewpoint on the basins' formations. From the field evidences it was clarified that the Green-Tuff sedimentary basins were formed by the collapsing movements closely connected with magmatic activities. The field evidences for collapse being the primary cause for basin formation are as follows: (1) The basal conglomerates consist mainly of the debris and fine rock fragments derived from the adjacent basement rocks. The lithofacies of the conglomerates is similar to that of talus or fanglomerate deposits. They abut against the basement, and the unconformity is represented by a straight line on the geological map. (2) Numerous consolidated fractures or sheared zones in the basement are recognized, and they are covered by the Neogene system. (3) The igneous activities occurred after the accumulation of the basal conglomerates, and the pyroclastics abut against the same conglomerates. Judging from the above field evidences, it was inferred that, prior to the deposition of the Green-tuff formation, the collapsed basins were formed due to the faults which were thrown down to the basin side. And also it is likely that the collapse subsequent to the uplift of the basement, is ascribed to a deep-seated crustal movement connected closely with the activity ofmagma. In the 1980's, some experiments were made, and consequently the relationship of the basin formation and the magmatic activities is fairly well clarified. As for the Green-tuff movement, there are some unsolved problems as follows: (1) The subsidence of the basins through the Green-Tuff movement. (2) The time-range of the Green-tuff movement. (3) The mechanism of the deep seated fractures causing the violent igneous activities. (4) The restoration of the palaeo-stress field concerning the formation of the basins, and also the change of the stress field through the Green-tuff movement.
日本地質学会の論文
1985-03-30

グリーンタフ変動の諸問題

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