内弧における造盆運動と広域テクトニクス　北部九州の第三紀堆積盆を例として

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タイトル別名
  • Role of the Plate-motions on the Development of Inner Arc Basins as Exemplified by the Tertiary of North Kyusyu.
  • ナイ コ ニ オケル ゾウボン ウンドウ ト コウイキ テクトニクス ホクブ
  • 北部九州の第三紀堆積盆を例として

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The purpose of this paper is to clarify the relation of development of the Tertiary inner arc basins in north Kyushu with the plate tectonics.<BR>Sedimentary bodies of inner arc basins must afford better foundation for basin analysis than those of the accretion zone bacause of weaker tectonic disturbance. The Tertiary basins in north Kyushu are chosen for an example. The basins are chronologically analysed for two particular items, i.e. migration of basins and changes of subsidence-velocity, which respectively reveal one feature of tectonics and must serve for regional correlation of tectonic phases.<BR>On the basis of the correlation of the strata, chronologically spanning from the early Eocene to the late Middle Miocene (55-10 Ma), dates of onset, termination and migration of sedimentary basisns are first checked. Secondly mean subsidence-velocities for one stage or substage are calculated for each basin employing hitherto published thickness-data.<BR>The Tertiary basin in north Kyushu first appeared in and around Amakusa and thereafter migrated north-and northeastward accompanied by termination of subsidence of old basins and birth of new ones. Dates of onset of notable migration are referred to 55 Ma, 49 Ma, 43 Ma and 37 Ma.<BR>Comparison of mean subsidence-velocities clarified two facts. While mean subsidence-velocity for any stage or substage remarkably differs from basin to basin, patterns of velocity-changes in chronologic series are quite harmonious among the basins. The latter fact suggests that the subsidence of basins is controlled by regional tectonics beyond the extent of each basin. The general pattern of serial velocity-changes is cyclic repeatition of the early phase of higher velocity and the succeeding phase of lower velocity and of longer duration. Four cycles are recognized separated by marked increase of subsidence-velocity (velocity jump). Dates of the four velocity jumps are referred to 55 Ma, 37 Ma, 39 Ma and 17 Ma, of which the former two dates chronologically coincide with two of the migration events. Synchronism of different kinds of events suggests tectonic importance of 55 Ma and 37 Ma.<BR>Rea et al. (1990), Aubry et al. (1988), Caress et al. (1988) etc. claim that the most distinct global environmental change throughout the Tertiary caused by reorganization of plates occurred at and around 55 Ma. 37 Ma is also regarded by several researchers (Scotese et al., 1988 ; Hag et al., 1987 ; Shackleton, 1986 etc.) as another phase of a global environmental change involved reorganization of plates. It must be noted that velocity jumps of basin subsidence are also documented at 55 Ma and 37 Ma in the marginal basins of the South China Sea (Ru and Pigott, 1986).<BR>The third velocity jump (30 Ma) is synchronous with the beginning of the spreading of the Shikoku basin (Uyeda and Kanamori, 1979). The fourth velocity jump (17 Ma) chronologically corresponds with the crockwise rotation of Southwest Japan (Otofuji and Matsuda, 1983, 1984) just after the termination of spreading of the Tsushima basin (Chough and Barg, 1987) and the Shikoku basin (Uyeda and Kanamori, 1979). Overview of the above noted facts shows a clear tendency that the older velocity jumps correspond with global tectonic events and younger ones do with more provincial or local events.<BR>Considering the present accuracy level of chronology of the tectonic events both of the inner arc basins and ocean plates, the above mentioned obvious coincidence among major events of both sides strongly suggests that the coincidence is not accidental, but the correponding events are linked together by causal relation. If this is the case, confirmed date of any basin event, whose counter event has hitherto unknown for the ocean plates, may forecast the latter.

収録刊行物

  • 地学雑誌

    地学雑誌 102 (7), 849-867, 1993

    公益社団法人 東京地学協会

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