Lower Cretaceous Strata Covering the Abyssal Tholeiite (The Hidaka Western Greenstone Belt) in the Chiroro Area, Central Hokkaido, Japan

Kiminami, Kazuo; Kontani, Yoshihiro; Miyashita, Sumio

doi:10.5575/geosoc.91.27

Cited by 21 publications

(17 citation statements)

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“…The TiO 2 contents range from 0.9 wt% to 1.3 wt% and P 2 O 5 from 0.07 wt% to 0.09 wt%. These characteristics are common with greenstones from the Lower Sorachi Ophiolite in the Sorachi‐Yezo Belt ( Ishizuka 1981; Kiminami et al 1985 ; Niida 1992; Nagahashi & Miyashita 1997; Fig. 10b).…”

Section: Petrographic Characteristicsmentioning

confidence: 83%

“…(b) TiO 2 versus FeO*/MgO plot for tholeiitic greenstones of the B‐Unit and PT‐Unit, compared with the Lower Sorachi Ophiolite and the Hidaka Belt greenstones. Po, Poroshiri Ophiolite ( Miyashita 1983); To, Tomuraushi ( Miyashita & Katsushima 1986); Ho, Horokanai Ophiolite ( Ishizuka 1981); Ch, Chiroro ( Kiminami et al 1985 ); Fu, Furano ( Niida 1992).…”

Section: Petrographic Characteristicsmentioning

confidence: 99%

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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: Petrographic Characteristicsmentioning

confidence: 83%

Section: Petrographic Characteristicsmentioning

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 eruption (formation) age of the greenstones in the Lower Sorachi Group is considered to be Late Jurassic from radiolarians in overlaying chert, shale and mudstone (Ishizuka et al . 1983b; Kiminami et al . 1985, 1992; Kito 1987, 1997; Kawaguchi 1997).…”

Section: Outline Of the Geology Of The Lower Sorachi Groupmentioning

confidence: 99%

“…The Lower Sorachi Group is mainly composed of greenstones (Kito 1987) that are conformably overlain by bedded chert. The greenstones show geochemical signatures broadly identical to mid‐oceanic ridge basalt (MORB) (Ishizuka 1981a; Kiminami et al . 1985; Kito et al .…”

Section: Introductionmentioning

confidence: 99%

Petrology of the greenstones of the Lower Sorachi Group in the Sorachi–Yezo Belt, central Hokkaido, Japan, with special reference to discrimination between oceanic plateau basalts and mid‐oceanic ridge basalts

Nagahashi¹,

Miyashita

2002

Island Arc

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The Lower Sorachi Group of the Sorachi–Yezo Belt in central Hokkaido, Japan is a peculiar accretionary complex characterized by numerous occurrences of greenstones (metabasalts and diabases), which are mostly composed of aphyric basalts. Clinopyroxene‐rich phenocryst assemblage in phyric basalts is different from olivine–plagioclase assemblage in mid‐oceanic ridge basalts (MORB). The greenstones are geochemically uniform, and show a lower‐Ti trend than MORB in an FeO*/MgO‐TiO2 diagram, mostly plotting on the island arc tholeiite (IAT) field in a TiO2−10MnO−10P2O5 diagram. In a MORB‐normalized spider diagram, the greenstones show a flat pattern from P to Y, which are lower than those of normal mid‐oceanic ridge basalt (N‐MORB). These indicate that the greenstones were derived by a higher degree of partial melting from a depleted mantle similar to a N‐MORB source, and experienced olivine–clinopyroxene fractional crystallization. However, a positive spike of Nb in the spider diagram cannot be explained, and may be attributed to mantle heterogeneity. These characteristics are analogous to those of oceanic plateau basalts (OPB) such as in Ontong Java Plateau, Manihiki Plateau and Nauru Basin, suggesting that the greenstones in the Lower Sorachi Group are of oceanic plateau origin. The present study proposes new field divisions to distinguish OPB from MORB in the conventional FeO*/MgO–TiO2 and TiO2−10MnO−10P2O5 diagrams.

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“…1) (Miyashita et al, 1994) (Hashimoto, 1975;Miyashita et al, 1994) (Hashimoto, 1975;Kagami, 1994) ( 1967;Komatsu, 1974Komatsu, , 1975Furusho and Kanagawa, 1999) ( Kiminami et al, 1985;Kiyokawa, 1992;2001; 1999) (Yagi et al, 1968;Bamba et al, 1969;1972, 1980Katoh and Niida, 1983) III. Leake et al (1997) magnesiohornblende (Mg ) edenite ( ), (Fig.…”

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confidence: 99%

Petrology of a peculiar amphibolite boulder rich in deep vivid green-colored amphibole porphyroblast from Hidaka Town, Hokkaido, Japan

Morishita¹,

Arai²,

Tamura³

et al. 2008

Japanese Magazine of Mineralogical and Petrological Sciences

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A peculiar amphibolite rich in deep vivid green colored amphibole porphyroblast was found as a boulder in the Chiroro River of Hidaka Town, Hokkaido, Japan. The amphibolite mainly consists of deep vivid green colored amphibole (porphyroblast), colorless amphibole (matrix) and plagioclase with a small amount of chlorite, epidote and chromian spinel. Deep vivid green colored amphibole porphyroblast is more than 20 modal % in the rock. Chromian spinel rarely occurs as inclusions in deep vivid green colored amphibole porphyroblast. The Cr 2 O 3 content of the deep vivid green colored domain is usually ~1 wt% (up to 2.5 wt% nearby chromian spinel) whereas that of colorless amphibole in the matrix is low, < 0.1 wt%. Deep vivid green colored amphibole porphyroblast is heterogeneous in chemical compositions within each grain and is divided into three domains as follows: (1) high Cr 2 O 3 (~1 wt%, up to 2.5 wt%) and Al 2 O 3 (> 10 wt%) green colored domain, (2) relatively high Cr 2 O 3 (~1 wt%) and low Al 2 O 3 (< 10 w%) green colored domain and (3) low Cr 2 O 3 (< 0.1wt%) and Al 2 O 3 (< 10 wt%) colorless domain. Chondrite normalized rare earth element (REE) patterns of both deep vivid green colored amphibole porphyroblast and colorless amphibole in the matrix are characterized by low light REE with positive Eu anomaly. The Cr#[= Cr/(Cr + Al) atomic ratio] and TiO 2 content of chromian spinel in the amphibolite are similar to those in a serpentinite complex of the Kamuikotan Zone. The amphibolite was formed by either amphibolitization of a rock containing chromian spinel derived from the surrounding serpentinite complex or extensively metasomatized serpentinite due to interaction with surrounding metamorphic rocks.

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Lower Cretaceous Strata Covering the Abyssal Tholeiite (The Hidaka Western Greenstone Belt) in the Chiroro Area, Central Hokkaido, Japan

Cited by 21 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

Petrology of the greenstones of the Lower Sorachi Group in the Sorachi–Yezo Belt, central Hokkaido, Japan, with special reference to discrimination between oceanic plateau basalts and mid‐oceanic ridge basalts

Petrology of a peculiar amphibolite boulder rich in deep vivid green-colored amphibole porphyroblast from Hidaka Town, Hokkaido, Japan

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