Differential timing of vertical-axis block rotations in the northern Ryukyu Arc: Paleomagnetic evidence from the Koshikijima Islands, Japan

Satoshi Tonai, Yusuke Suganuma, Juichiro Ashi, Tetsumaru Itaya, Hisashi Oiwane, Shoichi Kiyokawa

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1 Citation (Scopus)

Abstract

Over 300 samples for paleomagnetic analysis and K-Ar dating were collected from 27 sites at NW-SE and NE-SW trending dike swarms (herein, NW dikes and NE dikes, respectively) in the Koshikijima Islands, northern Ryukyu Arc. The NW dikes are Middle Miocene in age and have directions (D=-37.7°, I=51.8°, α95=9.6°, and κ=40.8) that are deflected westward relative to the stable eastern Asian continent. Conversely, the NE dikes, of Late Miocene age, have directions (D=16.1°, I=57.7°, α95=7.1°, and κ=41.9) that show no such deflection. These differences are interpreted as indicating that the Koshikijima Islands underwent approximately 40° of counter-clockwise rotation during the Middle to Late Miocene. A synthesis of the paleomagnetic and structural data suggests a three-stage history of extensional deformation: (1) displacement upon normal faults (F1 faults) without vertical-axis block rotation, (2) strike-slip reactivation of F1 faults and oblique-normal displacement on NE-SW-trending faults (F2 faults) with vertical-axis block rotation, and (3) oblique-normal displacement on F2 faults without vertical-axis block rotation. Regional differences in the timing and amount of counter-clockwise vertical-axis block rotations indicate that the northern Ryukyu Arc rotated as several distinct rigid blocks.

Original languageEnglish
Pages (from-to)71-84
Number of pages14
JournalTectonophysics
Volume497
Issue number1-4
DOIs
Publication statusPublished - Jan 2 2011

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth-Surface Processes

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