Chapters authored
Cretaceous Research: Paleolatitudes and Northward Migration of Crustal Fragments in the NW Pacific Inferred from Paleomagnetic Studies
Lateral migration of the Oshima and Sorachi-Yezo Belts within south central Hokkaido was quantitatively evaluated by means of paleomagnetic analyses in order to identify allochthonous blocks on the northwestern Pacific margin. The remanence stability of the Late Jurassic to Early Cretaceous voluminous igneous succession of the Kumaneshiri and Sorachi Groups and the overlying forearc sediments of the Cretaceous Yezo Group was evaluated through rock magnetic experiments. Twelve of the sites yielded characteristic primary components residing in mixtures of titanomagnetite and hematite having various mixing ratios. After an appropriate correction of inclinations’ shallowing of the post-depositional detrital remanent magnetization (pDRM) based on anisotropic acquisition experiments of the isothermal remanent magnetization (IRM), we confirmed significantly shallow inclinations even for the flattening-corrected data set, implying northward transportation after the emplacement. Based on comparisons to expected paleomagnetic directions calculated from contemporaneous reference poles, we conclude that the allochthonous blocks, including south central Hokkaido, migrated northerly during the Early Cretaceous. Previous investigations of paleomagnetism and numerical modeling of burial processes of sedimentary basins indicate that some crustal blocks in Hokkaido and NE Japan experienced delayed transportation and eventually amalgamated with the mother continent by the end of the Paleogene.
Part of the book: Dynamics of Arc Migration and Amalgamation