HR: 1330h
AN: T12C-0472    [PDF]
TI: Shortening deformation of the back-arc rift basin in the central northern Honshu, Japan
AU: * Kato, N
EM: naoko@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Universuty of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Sato, H
EM: satow@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, Universuty of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo, 113-0032 Japan
AB: The Pacific plate is being subducted beneath northern Honshu, Japan, forms a classical example of trench-arc-back arc system. The compressional stress, perpendicular to the northern Honshu arc, has produced the shortening deformation in the Miocene back arc rift basins since the Pliocene. Two narrow up-rift zones run parallel to the arc: Dewa hills on the west and Ou Backbone range on the east in the central part of northern Honshu. Active reverse faulting and folding are widely observed in this area. In spite of the large amount of data, the mechanisms and processes of this crustal shortening is poorly understood. As the basic data to reveal above-mentioned problems, we made crustal scale, geologic cross sections across the Dewa hills, synthesizing available geologic and geophysical data, such as surface geology, drill core data and seismic sections. Reprocessing of industry seismic data also carried out to improve our sections. The geologic cross section were examined using balanced cross section technique. The shortening deformation is strongly controlled by pre-existing Miocene extensional structures. The uplift mechanisms of the Dewa Hills can be explained by the Miocene fault reactivation beneath the Dewa hills, using low-angle Miocene normal faults with shallow fat and deeper ramp. Due to the reverse faulting of Miocene pre-existed fault, asymmetrical structure was developed across the Dewa hills. On the western side of the Dewa hills 5-7 km of shortening was accommodated with wedge and emergent thrusting and fault-propagation fold in the back arc sediments. Low-angle detachment faults produced fault-related folds on their hanging wall are located in the middle to late Miocene mudstones. On the eastern side of the gentle folds are dominated and ca. 3 km of horizontal shortening is estimated. Judging from the onset of the shortening deformation (ca. 3 Ma), the averaged 3 mm/y of shortening is estimated across the Dewa hills.
DE: 0905 Continental structures (8109, 8110)
DE: 8100 TECTONOPHYSICS
DE: 8105 Continental margins and sedimentary basins
DE: 8110 Continental tectonics--general (0905)
DE: 9320 Asia
SC: Tectonophysics [T]
MN: 2003 Fall Meeting