Stratigraphic relation between greenstones and clastic sedimentary rocks in the Kamuikotan Belt, Hokkaido, Japan

Kito, Norio

doi:10.5575/geosoc.93.21

Cited by 26 publications

(15 citation statements)

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“…In spite of the lithologic similarity to the Lower Sorachi Ophiolite, the B‐Unit greenstones are separated into several slabs, alternating with greenstone‐dominant mixed facies of the MN‐Unit and have no stratigraphic continuity with the Nitarachi‐Yezo Sequence to the west ( Figs 2,15). The basal part of the sequence (Tithonian‐Berriasian S2 member, Kito 1987) is lacking in the Nitarachi‐Yezo Sequence. These differences in occurrence strongly suggest that the slab bodies of the B‐Unit do not comprise a coherent forearc sequence as do the Lower Sorachi Ophiolite occurrences, but represent large‐scale bodies tectonically sliced from the forearc Lower Sorachi Ophiolite and subsequently covered by the Nitarachi‐Yezo Sequence.…”

Section: Discussionmentioning

confidence: 99%

Accretion and tectonic erosion processes revealed by the mode of occurrence and geochemistry of greenstones in the Cretaceous accretionary complexes of the Idonnappu Zone, southern central Hokkaido, Japan

2000

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The Cretaceous accretionary complexes of the Idonnappu Zone in the Urakawa area are divided into five lithological units, four of which contain greenstone bodies. The Lower Cretaceous Naizawa Complex consists of two lithologic units. The Basaltic Unit (B‐Unit) is a large‐scale tectonic slab of greenstone, consisting of depleted tholeiite similar to that of the Lower Sorachi Ophiolite (basal forearc basin ophiolite) in the Sorachi‐Yezo Belt. The Mixed Unit of Naizawa Complex (MN‐Unit) contains oceanic island‐type alkaline greenstones which occur as slab‐like bodies and faulted blocks with tectonically dismembered trench‐fill sediments. Repeated alternations of the two units in the Naizawa Complex may have been formed by the collision of seamounts with forearc ophiolitic body (Lower Sorachi Ophiolite) in the trench. The Upper Cretaceous Horobetsugawa Complex structurally underlies the Naizawa Complex in its original configuration, and it also contains greenstone bodies. Greenstones in the MH‐Unit occur as blocks and sedimentary clasts in a clastic matrix, and exhibit depleted tholeiite and oceanic‐island alkaline basalt/tholeiite chemistry. This unit is interpreted as submarine slide and debris flow deposits. Greenstones in the PT‐Unit occur at the base of several chert‐clastic successions. Most of the greenstones are severely sheared and show normal‐type mid‐ocean ridge basalt composition. The PT‐Unit greenstones are considered to have been derived from abyssal basement peeled off during accretion. The different accretion mechanism of the greenstones in the Naizawa and Horobetsugawa complexes reflects temporal changes in subduction zone conditions. Seamount accretion and tectonic erosion were dominant in the Early Cretaceous, due to highly oblique subduction of the old oceanic crust and minimal sediment supply. Whereas, thick sediments with minor mid‐ocean ridge basalt and olistostrome accreted in the Late Cretaceous, due to near‐orthogonal subduction of young oceanic crust with voluminous sediment supply.

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Section: Discussionmentioning

confidence: 99%

Accretion and tectonic erosion processes revealed by the mode of occurrence and geochemistry of greenstones in the Cretaceous accretionary complexes of the Idonnappu Zone, southern central Hokkaido, Japan

2000

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“…The Sorachi Group contains numerous well-preserved radiolarian fossils, as detailed by a number of radiolarian biostratigraphic studies (Kito, 1987(Kito, , 1995Kito et al 1986;Minoura et al 1982;Okada et al 1991;Takashima, Nishi & Yoshida, 2001). From examining various areas in Hokkaido, these studies have identified three datum planes within the Sorachi Group.…”

Section: Radiolarian Biostratigraphy Of the Sorachi Groupmentioning

confidence: 99%

“…In ascending order, these planes are represented by the first occurrence of Pseudodictyomitra carpatica, the first occurrence of Cecrops septemporatus and the last occurrence of C. septemporatus (e.g. Kito, 1987Kito, , 1995Takashima, Nishi & Yoshida, 2001). These planes correlate to Kimmeridgian-Tithonian, Late Valanginian and Early Barremian times, respectively (Baumgartner et al 1995).…”

Section: Radiolarian Biostratigraphy Of the Sorachi Groupmentioning

confidence: 99%

Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan

2006

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-The Sorachi Group, composed of Upper Jurassic ophiolite and Lower Cretaceous island-arc volcano-sedimentary cover, provides a record of Late Jurassic-Early Cretaceous sedimentation and volcanism in an island-arc setting off the eastern margin of the Asian continent. Stratigraphic changes in the nature and volume of the Sorachi Group volcanic and volcaniclastic rocks reveal four tectonic stages. These stages resulted from changes in the subduction direction of the Pacific oceanic plate. Stage I in the Late Jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back-arc basin. Slab roll-back caused rifting and sea-floor spreading in the supra-subduction zone along the active Asian continental margin. Stage II corresponded to the Berriasian and featured localized trachyandesitic volcanism that formed volcanic islands with typical island-arc chemical compositions. At the beginning of this stage, movement of the Pacific oceanic plate shifted from northeastward to northwestward. During Stage III, in the Valanginian, submarine basaltic volcanism was followed by subsidence. The Pacific oceanic plate motion turned clockwise, and the plate boundary between the Asian continent and the Pacific oceanic plate changed from convergent to transform. During Stage IV in the Hauterivian-Barremian, in situ volcanism ceased in the Sorachi-Yezo basin, and the volcanic front migrated west of the Sorachi-Yezo basin.

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“…In the Kamuikotan zone, sedimentation ages indicated by radiolaria from black or grey shales of the melange units are early Cretaceous, from Valanginian to Barremian or Aptian (Ishizuka et al 1984;Watanabe and Maekawa 1985;Hori and Sakakibara 1994) and radiolaria in chert show late Triassic to early Cretaceous ages (Watanabe 198 1;Hori and Sakakibara 1994). Radiolarian fossils from chert overlying the ophiolites (Horokanai ophiolite and Sorachi greenstones) are from Late Jurassic to Early Cretaceous, up to Valanginian or Barremian in age (Ishizuka et al 1983b;Kiminami et al 1986;Kito 1987). All these rocks are overlain structurally by forearc basin sedimentary rocks, the Yezo Supergroup (Matsumoto and Okada 1971;Okada 1974;Kanie et al 1981;Kiminami et al 1985;Kito 1987).…”

Section: B Tectonic Significance Of the Young K-ar Agesmentioning

confidence: 99%

“…Radiolarian fossils from chert overlying the ophiolites (Horokanai ophiolite and Sorachi greenstones) are from Late Jurassic to Early Cretaceous, up to Valanginian or Barremian in age (Ishizuka et al 1983b;Kiminami et al 1986;Kito 1987). All these rocks are overlain structurally by forearc basin sedimentary rocks, the Yezo Supergroup (Matsumoto and Okada 1971;Okada 1974;Kanie et al 1981;Kiminami et al 1985;Kito 1987). The Middle Yezo Group is unconformable in part on the Lower Yezo Group.…”

Section: B Tectonic Significance Of the Young K-ar Agesmentioning

confidence: 99%

Palaeogene K‐Ar ages from the Kamuikotan metamorphic rocks, southern area of the Kamuikotan Gorge, central Hokkaido, northern Japan

et al. 1995

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Mica separates from 44 metamorphic rocks (mostly pelitic) from the southern area of Kamuikotan Gorge, central block of the Kamuikotan zone were dated using the K-Ar method. The ages of white micas, separated from pelitic schists, range from 51 to 74 Ma. The Palaeogene K-Ar ages are supported by 40Ar-39Ar dating. Judging from mineral paragenesis and X-ray diffraction studies (RM values) of white micas, most of the pelitic schists belong to the intermediate pressure type. In the Orowen River district, the northern part of the study area, biotite from metavolcanic rocks of a lower pressure assemblage yields the youngest K-Ar ages (45-50 Ma). Although the Kamuikotan zone was considered to have been a subduction-related metamorphic belt along a Mesozoic consuming margin, the time span of the metamorphism and the lowering of metamorphic pressure in younger rocks suggest that: (1) exhumation of the younger Kamuikotan rocks accompanied the erosion of forearc basin sediments (the Yezo Supergroup); (2) the increase in the thermal gradient was probably related to the approach of the Kula-Pacific ridge to the subduction zone; and (3) the main stage of exhumation of the Kamuikotan rocks ceased before westward movement of the Pacific plate, which induced the collision of the Hidaka-Nemuro belts (palaeo-Kurile arc-trench system) with the Kamuikotan zone.

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Stratigraphic relation between greenstones and clastic sedimentary rocks in the Kamuikotan Belt, Hokkaido, Japan

Cited by 26 publications

References 0 publications

Accretion and tectonic erosion processes revealed by the mode of occurrence and geochemistry of greenstones in the Cretaceous accretionary complexes of the Idonnappu Zone, southern central Hokkaido, Japan

Accretion and tectonic erosion processes revealed by the mode of occurrence and geochemistry of greenstones in the Cretaceous accretionary complexes of the Idonnappu Zone, southern central Hokkaido, Japan

Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan

Palaeogene K‐Ar ages from the Kamuikotan metamorphic rocks, southern area of the Kamuikotan Gorge, central Hokkaido, northern Japan

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