知多半島の中新統師崎層群の堆積時造構造運動

抄録

In the Miocene Morozaki Group of the Chita Peninsula, there are two types of fold generated under different stresses : left-stepping en echelon fold developed along the southwest coast of the Peninsula, and east-west-trending folds which are found in the east and northwest of this area. The former is a set of folds produced by left-lateral strike slip of the Atsumiwan Fault which is a splay fault at the end of the Median Tectonic Line, extending along the southwest coast of the Peninsula. The latter are folds related to right-lateral strike slip of the Chitawan and Isewan Faults, splay-faults of the Yoro-Isewan Fault which forms conjugate fault set with the Median Tectonic Line.
On the basis of the commonly expressed concept that synsedimentary folding has a relation with the thickness of the deposits in the sedimentary basin. Investigation for the lateral variation in thickness of the four major sandstone beds revealed that there are three phases of faulting during the deposition of the Morozaki Group and in the following age of emergence.
1) Right-lateral slip phase of the Chitawan Fault.
This phase is contemporaneous with sedimentation of the Himaka, Katana and Toyohama Formations, being characterized by the development of E-W trending folds and E-W or N-S trending elastic dikes.
2) Left-lateral slip phase of the Atsumiwan Fault.
These faulting occurred concurrently with the deposition of the Yamami and Utsumi Formations, being related to the development of the left-stepping en echelon fold, the rightstepping en echelon sandstone-dike swarms, the Tsubuteura Olistostrom, the Hazikami Fault and the Utsumi Growth Fault.
3) Right-lateral slip phase of the Isewan Fault.
It is the phase of emergence following the deposition of the Utsumi Formation, and the E-W trending folds in the north of Utsumi were caused by these faulting.
It is conclusded from the results of this investigation that the sedimentation and tectogenesis of the Morozaki Group took place under the alternating faulting of the Median Tectonic Line and Yoro-Isewan Fault Systems which are in a conjugated relation.