Skip to Main Content
Book Chapter

Emplacement of a layered mafic intrusion in the Shimanto accretionary complex of southwest Japan: Evidence from paleomagnetic and magnetic fabric analysis

By
K. Kodama
K. Kodama
Research Center for Knowledge Science in Cultural Heritage, Doshisha University, Kyotanabe, Kyoto 610-0394, JapanCenter for Advanced Marine Core Research, Kochi University, Nankoku, Kochi 783-8502, Japan
Search for other works by this author on:
T. Byrne
T. Byrne
Center for Integrative Geosciences, University of Connecticut, Storrs, Connecticut 06269, USA
Search for other works by this author on:
J.C. Lewis
J.C. Lewis
Geoscience Department, Indiana University of Pennsylvania, Indiana, Pennsylvania 15705, USA
Search for other works by this author on:
J.P. Hibbard
J.P. Hibbard
Department of Marine, Earth, and Atmospheric Science, North Carolina State University, Raleigh, North Carolina 27695, USA
Search for other works by this author on:
M. Sato
M. Sato
National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan, Tsukuba, Ibaraki 305-8567, Japan
Search for other works by this author on:
T. Koyano
T. Koyano
Sansho Shigyo Co. Ltd., Tokyo 101-0046, Japan
Search for other works by this author on:
25 September 201723 April 2018

ABSTRACT

A 200-m-thick, near-vertical, middle Miocene (ca. 14 Ma), gabbroic sheeted intrusion in the Muroto area of the Shimanto accretionary complex of southwest Japan yields anisotropy of magnetic susceptibility (AMS) showing a magnetic foliation for the minimum axis (Kmin) oblique (by ~70°) to the perpendicular of the intrusive contact. Assuming the Kmin axis represents the paleovertical axis, these data suggest that the gabbroic sheet was not intruded into the host sediments horizontally. Paleomagnetic measurements of the gabbroic intrusion show an in situ mean direction of reversed polarity (declination/inclination [Dec/Inc] = 287°/–65°, α95 = 3°) that is considerably different from the expected, reversed-polarity dipole-field direction of this region (Dec/Inc = 0°/–56°). A structural analysis combining the paleomagnetic and AMS data led to the determination of a unique pole of rotation, around which the dike can be back-rotated to its initial orientation. The magnitude of rotation necessary for the in situ paleomagnetic direction to be back-rotated to the expected direction is ~60°, which is consistent with the rotation required for the Kmin axis to be vertical. This consistency can be regarded as independent support for our interpretation of the AMS results and the reliability of the paleomagnetic data. Consequently, we propose that the Muroto gabbro was intruded when the paleo–trench-fill sediments had been tilted landward by ~20°, presumably by accretion, and that the gabbro might have been intruded as a sill-like sheet along a structurally weak zone, possibly part of the frontal thrust plane in the Shimanto accretionary prism.

You do not currently have access to this article.
Don't already have an account? Register

Figures & Tables

Contents

GSA Special Papers

Geology and Tectonics of Subduction Zones: A Tribute to Gaku Kimura

Geological Society of America
Volume
534
ISBN electronic:
9780813795348

GeoRef

References

Related

A comprehensive resource of eBooks for researchers in the Earth Sciences

This Feature Is Available To Subscribers Only

Sign In or Create an Account

This PDF is available to Subscribers Only

View Article Abstract & Purchase Options

For full access to this pdf, sign in to an existing account, or purchase an annual subscription.

Subscribe Now