QUATERNARY CRUSTAL MOVEMENTS ESTIMATED FROM DEFORMED TERRACES AND GEOLOGIC STRUCTURES OF THE KAMIKITA COASTAL PLAIN, NORTHEAST JAPAN

DOI Web Site Web Site 19 Citations 1 References

Bibliographic Information

Other Title
  • 上北平野の段丘と第四紀地殻変動
  • 上北平野の段丘と第4紀地殻変動
  • カミキタ ヘイヤ ノ ダンキュウ ト ダイ4キ チカク ヘンドウ

Search this article

Abstract

The Kamikita coastal plain is situated on the Pacific coast of Northeast Japan and belongs to the outer belt of Northeast Japan arc. The Ou backbone range runs along its arc in the west side of the plain and the Kitakami mountains lie to the south of the plain (Fig. 1). This plain extends about 50 km from north to south, reaching a width of 30 km (Fig. 2). The southwest area of the plain is hills composed of Neogene formations (Fig. 3), the summit plane of which is 200 m to 400 m high above sea level. Furthermore, around the Kitakami mountains the erosional surfaces with low relief are developed, which are 400 m to 600 m high above sea level.<br> Marine and fluvial terraces are fairly well developed on this plain. These terraces are extensively covered with Quaternary tephras derived mainly from Towada and Hakkoda volcanoes on the Ou backbone range (Fig. 5). By geomorphological and tephrochronological methods, the marine terraces are classified into at least four levels, i. e., Higher, Shichihyaku, Tengutai and Takadate surfaces in descending order; and fluvial terraces into five levels i. e., Takadate, Nejo, Shibayama, Shichinohe and Sanbongi surfaces in descending order (Fig. 7). There are most likely marine surfaces that are correlated with Nejo and Shiba yama surfaces in the plain.<br> The topographical features and terrace-making deposits of the latter three marine surfaces show that each surface was formed during different periods of transgression. Takadate surface, the most well-preserved one among them, is estimated to have been formed at the culmination of the last interglacial stage from its topographical features, terrace-making deposits and the oldest ages of tephra overlying it. Assuming that the accumulation rate of tephra and the tilting rate of marine surfaces have been nearly constant after the formation of terrace, it is estimated that Higher surface was formed ca. 430_??_470 ka B. P., Shichihyaku surface ca. 220_??_330 ka B. P, and Tengutai surface ca. 160_??_200 ka B. P.. Similarly, it is estimated that Nejo surface was formed ca. 80_??_100 ka B. P. and Shibayama surface ca. 50_??_70 ka B. P. from the age estimation based on the above assumption. Shichinohe and Sanbongi surfaces are thought to have been formed ca. 25, 000y. B. P. and ca. 13, 000 y. B. P. respectively from the 14C ages of tephras overlying them (Fig. 6). <br> Figure 12 shows the Quaternary crustal movements estimated from the change of former shoreline heights (Figs. 7 and 11), deformed fluvial terrace surfaces (Fig. 10) and geologic structure of bedrock (Fig. 4) in this region.<br> 1. The western margin of the plain was differentiated from the Ou backbone range or the hills by the reverse faulting and flexing in the early stage of the Quaternary. However, the faulting along the northwestern margin of the plain has not been active after the formation of Shichihyaku surface, while the flexing along the southwestern margin of the plain has been continuously active since the end of the Pliocene to the late stage of the Quaternary.<br> 2. The whole area of the plain has been uplifted at least since the formation of Higher surface judging from the development of marine terraces with different ages and heights. The estimated maximum rate of uplift is 0.3 mm/yr during the last 120 ka. From the regional change of each former shoreline height, the gentle E-W trending foldings with the wave length of about 15 km are found in the northern half of the plain and the northward tilting with NNW-SSE trending anticlinal movement in the southern half of the plain. It is interpreted that the nearly N-S trending and flexing indicate the crustal shortening under the influence of the horizontal maximum compressional stress (σHmax=σ1) which is prominent in Northeast Japan during the Quaternary. Wheares it is difficult to ascribe the E-W trending foldings to the same stress field.

Journal

Citations (19)*help

See more

References(1)*help

See more

Keywords

Details 詳細情報について

Report a problem

Back to top