The nature of faulting and deformation in the Mineoka ophiolite, NW Pacific Rim

Akiko Takahashi, Yujiro Ogawa, Yasufumi Ohta, Naoto Hirano

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


A belt of disrupted ophiolitic rocks occurs on the Boso Peninsula (Japan), currently located north of the oblique subduction boundary between the Philippine Sea and North American Plates, under which the Pacific Plate has been subducting westwards. This ophiolitic belt (Mineoka Belt) is composed of mafic-ultramafic rocks together with Tertiary chert and limestone and island-arc volcaniclastic rocks. Our detailed structural studies in and around the basaltic rock bodies within the ophiolite reveal three phases of deformation. The first phase is further divided into three stages, all related to oblique normal faulting associated with extensional tectonics at or near a spreading axis. Fluid pressures appear to have fluctuated in association with faulting and veining during this phase. The second phase of deformation is characterized by thrust-related shear zones with a significant strike-slip component and is probably related to the final emplacement of the ophiolite by oblique subduction-obduction processes. The third and final phase of deformation affected not only the ophiolite but also later terrigenous and island-arc pyroclastic rocks. This deformation involved large-scale transpressional dextral slip on forearc sliver faults, which are still active today.

Original languageEnglish
Pages (from-to)299-314
Number of pages16
JournalGeological Society Special Publication
Publication statusPublished - 2004 Jun 23
Externally publishedYes

ASJC Scopus subject areas

  • Water Science and Technology
  • Ocean Engineering
  • Geology


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