Sedimentation and Tectonics of Zenisu Ridge, Eastern Nankai Trough and Suruga Trough Regions
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概要
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Great amounts of terrigenous sediments have been deposited as trough wedge sedimentary layers in the Suruga Trough and the Eastern Nankai Trough since the late Pliocene. Trough wedge sedimentary layers show some cyclic sedimentation correlating with the block collision. The cycle has originated from an intence uplift of land with the block collision and ended in the deformation of trough-fill layers with the plate subduction. In one cycle, an unconformity has been formed in the region around the uplifted mass and in the trough region. Although the unconformities originally relate to the tectonic movement due to one block collision, these are out of phase in time between the two regions. The unconformity in the trough region is younger than the one in the landward region because sediment transportation requires a duration. This cyclic sedimentation is recognized at two times since the Pliocene. One has originated from the Tanzawa block collision in the early Pliocene, and the other has begun at the Izu block collision since the middle Pleistocene. Characteristic intraplate deformation with backthrusts has important effects on the formation of unconformity and sedimentary basin, and on the deformation of trough-fill layers. The active subduction zone has migrated seaward from the present trough region. The trough-fill sediments have been transported by turbidity currents through the Nankai Deep Sea Channel. Main source areas of these sediments are the Fuji and Kano River regions and the Tenryu River region which are situated on the Southern Fossa Magna. The Nankai Deep Sea Channel has developed as a main passing way of these sediments and has been formed by turbidity currents. This channel shows the typical meandering pattern and channel migration and its topography closely resembles subaerial river topography. The meandering pattern has been strongly controlled by the slope of trough floor which is on the convergent plate boundary. The rapidly decreasing sedimentation rate of trough-fill sediments in the late Pleistocene reflects the dam-up effects of deformed trough-fill layers, intraplate deformation and the Izu Spur collision in the last cycle of the trough sedimentation.Eastern Nankai TroughSuruga TroughZenisu RidgeNankai Deep Sea Channeltrench sedimentationtectonicsplate collision zone
- 東北大学の論文
- 1988-03-25