Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination. (17th December 2019)

• Record Type: Journal Article
• Authors: Katagiri, Takahiro; Naruse, Hajime; Ishikawa, Naoto; Hirata, Takafumi
• Is Part Of: Island arc. Volume 29:Number 1(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-12-17
• Subjects: arc–arc collision -- Paleo‐Kuril Arc -- paleomagnetism -- U–Pb radiometric dating; Plate tectonics -- Periodicals; Island arcs -- Periodicals; Geodynamics -- Periodicals; 551.136
• DOI: 10.1111/iar.12329
• Languages: English
• ISSNs: 1038-4871

Abstract

Abstract: The Paleo‐Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo‐Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo‐Kuril arc‐trench system, paleomagnetic surveys and U–Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka‐hill region, eastern Hokkaido. The U–Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka‐hill region experienced a 28° clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62°) but larger than that of the overlying Onbetsu Group (−9°). It is thus suggested that the Shiranuka‐hill region experienced a clockwise rotation of approximately 34° between the deposition of the Nemuro and Urahoro Groups (50–39 Ma), and a 38° clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39–34 Ma). The origin of the curved tectonic belt of the Paleo‐Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka‐hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc–arc collision induced the bent structure of the western Paleo‐Kuril Arc. Abstract : Paleomagnetic analysis in the Urahoro Group and radiometric dating, using U–Pb, of zircons extracted from tuffaceous beds, were conducted. Our data indicated a 29° clockwise rotation of the Shiranuka‐hill region after 39 Ma. The age constraints of the block rotation supports the hypothesis that the collision between the Paleo‐Kuril Arc and Paleo‐Northeastern Japan Arc caused the rotation of the tectonic blocks in the Paleo‐Kuril Arc. Abstract : 北海道東部に分布する根室帯および常呂帯の地層トレンドは，その西縁部において屈曲する. すなわち，釧路湿原を挟んで東側に露出する地層は東西 走向を示すが，西側に露出する地層は南北走向を示す. 西側の地層から東偏した古地磁気偏角が得られることから，地層トレンドの違いは西側部分が時計回り回転をした結果であると解釈されてきた. この回転運動に対して年代的な制約を与えるため始新統浦幌層群の古地磁気偏角とU–Pb年代を測定したところ，浦幌層群の堆積年代はおよそ39 Maであり，釧路湿原西側では約28°の時計回り回転を示すことが判明した. 上位および下位の地層で得られた古地磁気偏角と比較すると，本地域の回転運動は浦幌層群堆積の前後でおこったと解釈される. 屈曲構造の形成年代に関するこの制約は，屈曲構造が古千島弧と古東北日本弧の衝突に由来することを示唆する.