Hidaka Super Gr

Hidaka Belts (main part)

Synonym:

Northern parts of the belt comprise zones with differing structural trends (north-south v. NE-SW: Tajika 1989, 1992) bounded by faults and shear zones (Watanabe & Kimura 1987). In addition to the dominant occurrence of mudstone and turbidite sandstones, lesser amounts of green and red mudstones, basalts, conglomerate, and chaotic mélange facies including blocks of chert and limestone also occur.

Except for Cretaceous deposits in the western marginal zones, here assigned to the Idonnappu Zone, Paleocene- Eocene radiolarians have been reported from hemipelagic and terrigenous mudstones in central to eastern parts of the belt (Watanabe & Iwata 1985; Kiminami et al. 1990a: Taiika & Iwata 1990).

These older rocks, including Late Cretaceous mudstone, are considered as sedimentary blocks derived from the Idonnappu Zone in the west (Tajika & Iwata 1990).

The Hidaka Belt accretionary complexes are occasionally accompanied by basalt and dolerite. They show field relationships suggestive of synsedimentary in situ eruption and intrusion into unconsolidated terrigenous mudstone and sandstone (Mariko 1984; Mivashita & Katsushima 1986; Kiminami et al. 1999; Nakayama 2003), as represented by inter-pillow mudstone, silicified baked margins of mudstones in contact with dolerite and mudstone fragments involved in dolerites.

Radiolarians from mudstones originally thought to be Late Cretaceous in age (Taiika & Iwata 1983; Watanabe & Iwata 1987; Iwata & Tajika 1989) have been re-assigned to the early Paleocene by Tajika (1992), reflecting subsequent progress in early Paleogene biostratigraphy.
Permian fusulinids (Endo & Hashimoto 1955) and Triassic holothurians sclerites (Iwata et al. 1983a) have been identified in limestone clasts and blocks, and the age of chert blocks ranges from Late Triassic to mid-Cretaceous (Tajika & Iwata 1983, 1990; Watanabe & Iwata 1987; Iwata & Tajika 1989).

Geochemical studies indicate a mid-oceanic ridge basalt origin (Miyashita & Katsushima 1986; Mariko & Kato 1994; Miyashita & Yoshida 1994; Miyashita & Kiminami 19g9). Based on these characteristics, a seafloor spreading environment adjacent to a continent, either associated with continental margin rifting (Mariko 1984) or oceanic ridge subduction (Mivashita & Katsushima 1986), has been assumed for the origin of the basalt-sediment complex.

The Hidaka Belt is also characterized by intrusions of granitoid rocks and gabbro (Maeda et al. 1986). The zone of these intrusions within the non-metamorphic Hidaka Supergroup extends to the Hidaka Metamorphic Belt in the south (Hidaka Mountains), where deep crustal sections are exposed.