[S-CG61] Dynamics in mobile belts

[SCG61-P11] Structural evolution of the Nambayama and Tozaki Anticline based on fault-related fold modeling, Northern Fossa Magna, central Japan

*Naoki ITO¹, Tatsuya Ishiyama¹ (1.Earthquake Research Institute, Univ. of Tokyo)

Keywords:Northern Fossa Magna, fault-related fold , balanced cross section

The Northern Fossa Magna located between the NE Japan and the SW Japan is a rift basin associated with the opening of the Sea of Japan and later has experienced a large amount of shortening under compressional stress regime since the Pliocene. In this region, > 6 km thick sediments (JNOC) are strongly folded by the Nambayama and Tozaki Anticline. Meanwhile, deeper thrust fault trajectories responsible for structural growth of these folds remain poorly understood. In this study, we conducted fault-related fold analysis (e.g. Suppe, 1983; Suppe and Medwedeff, 1990; Allmendinger, 1998) using many geologic and geophysical data to define thrust fault trajectories responsible for the structural growth of the Nambayama and Tozaki Anticline. Based on compilation of surface geology, dip-strike data (e.g. Akabane and Kato, 1989), seismic reflection profiles and oil well stratigraphy (JNOC), we constructed balanced cross sections. We estimated the best-fit model of thrust trajectories and their activities to retrodeform geologic cross sections from the Takada Plain to the Sea of Japan coast by forward modeling in trial-and-error manner. We identify an east-dipping blind thrust below the Takada Plain which was active during ca. 5.7 to 3.9 Ma. At a depth of ca. 6 km, this blind thrust bifurcates into a concave-up thrust to the west, which has been responsible for the structural growth of the Nambayama Anticline. Additionally, we identify a west-dipping blind thrust in the further west side of the section, which has been responsible for the structural growth of the Tozaki Anticline.

References

Allmendinger, R. W. (1998). Tectonics 17, 640–656.
Akabane, S. and Kato, H. (1989). Geol. Surv. Japan, 89p.
Suppe, J. (1983). Am. J. Science., 283, 684-721.
Suppe, J. and Medwedeff, D. A. (1990). Eclogae Geol. Helv., 83, 409-454.
Woodward, N. B., Boyer, S. E. and Suppe, J. (1989). AGU, Vol. 6, 132 p.