**5.1. Stage 0 (Incipient rift stage; 35 – 20 Ma)**

resulted in basin inversion and uplift of both the eastern and western sectors of the Ou

Stage VI represents the uplift of the whole Backbone Range and the formation of an angular unconformity between the Hanayama and Yoshizawa Formations within the Yuda Basin (Figures 11, 12). The uplift of the Backbone Range during this stage resulted from "pop-up" of the sectors of the Backbone Range by activation of the Senya Fault system as well as reactivation of the Eastern Marginal Fault and Kawafune-Warikurayama Fault systems under intense

In this section, Late Cenozoic tectonic events deduced from developments of other fore-arc, intra-arc and back-arc basins across the northeast Japan transects were correlated with those in the Yuda Basin (Figure 13). Based on the results, Late Cenozoic tectonics in northeast Japan was clarified and was divided into seven stages from 0 to VI as described below. Then, the author will discuss the origin of regional tectonic events. The reviews presented herein could

**Figure 13.** A compiled chart showing correlation of tectonic movements across northeast Japan transect since 18 Ma (revised after [31]). Stages I-VI are tectonic stages defined in this study. Uc.: unconformity, cgl.: conglomerate. Com‐ piled after (a) [48] revised after new age model of [22], [49]; (b) [27-29]; (c) [27-29, 32]; (d) [32, 51-54]; (e) [31, 38,

Backbone Range (Figure. 12).

compression (Figure. 12)[40].

*4.3.6. Stage VI (Intense compression stage; 3~2 Ma - Present)*

172 Mechanism of Sedimentary Basin Formation - Multidisciplinary Approach on Active Plate Margins

**5. Late Cenozoic tectonic events in northeast Japan**

provide a revised Late Cenozoic tectonics model in northeast Japan.

55-56]; (f) [16, 33, 57-58]; (g) [56, 59-65]; (h) [31, 66-68]; (i) [31]

Stage 0 represents formation of the incipient rift system along the eastern margin of the Sea of Japan as already noted in section 3. Rift basins in this stage were relatively small and marine incursion was limited within a narrow zone along the present Sea of Japan coast [21]. The timing of marine incursion varied among rift basins [21], suggesting that individual marine basin was relatively short lived. The incipient rift basins had not directly developed into later syn-rift large basins, but were interrupted by regional unconformity during the late Stage 0

#### **5.2. Stage I (Syn-rift stage: 20 - 13.5 Ma)**

Syn-rift stage has been divided into two substages: IA and IB on the basis of tectonic conversion from wide rift mode to narrow rift mode [39], associated with a stress change from regional extension to coexistence of extension and compression at around 15 Ma.
