H. Tanaka et Y. Saka, BLOCK ROTATION BY BASEMENT STRIKE-SLIP FAULTING IN THE SANCHU GRABEN,CENTRAL JAPAN, Journal of structural geology, 15(8), 1993, pp. 1021-1032
In the Kanto Mountains, central Japan, Cretaceous fore-arc basin sedim
ents are sandwiched by basement rocks in a narrow zone traditionally c
alled the Sanchu graben. In the axial part of the graben they are divi
ded into numerous blocks by a series of subparallel sinistral strike-s
lip oblique faults (block faults). These blocks have rotated clockwise
together with block faults. Resulting clockwise deviation of strike o
f the strata from the general trend increases gradually from the margi
ns toward the axial part of the graben, where it attains 30-degrees. B
lock faults are traced in part of the graben where the strata show thi
s clockwise deviation of strike. The structural evidence and the high
length/width ratio of the rotated domain suggest that a major dextral
strike-slip fault lies beneath the Cretaceous cover of the axial part.
The unconformable boundary between the Cretaceous cover and the under
lying basement may have played the role of a detachment plane, and pre
vented the fault from extending into the cover. The rotation of the ov
erlying Cretaceous system is thus a superficial manifestation of under
lying dextral strike-slip faulting.