K-Ar ages and petrological characteristics of granitoid pebbles from the Eocene Beppo Formation in the Kushiro region, Hokkaido, Japan.

正継, 小笠原; 賢, 柴田; 茂, 内海

doi:10.5575/geosoc.104.516

Cited by 9 publications

(4 citation statements)

References 13 publications

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“…At Sikhote Alin, the rocks consist of rhyolite–dacite (mainly welded ash‐flow tuffs) and andesite. Granite and granodiorite with high K 2 O and (K 2 O + Na 2 O)/Na 2 O found in southeastern Korea and southwestern Japan are distinct from Paleo‐Kuril arc magmatism (Ogasawara, Shibata, & Uchiumi, ).…”

Section: Discussionmentioning

confidence: 98%

“…Ogasawara et al () report that igneous activity occurred around the Paleo‐Kuril arc between 76 Ma and 66 Ma, and Sakakibara et al () also suggested that the igneous activity ended before 65 Ma. However, biotite K–Ar ages of acidic tuff of 66.7 ±4.0 Ma and 54.0 ±3.4 Ma (2σ error) from the forearc basin sediment of the Nemuro Group (Shibata, ) may indicate that the igneous activity continued until the early Eocene (~54 Ma).…”

Section: Discussionmentioning

confidence: 99%

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U–Pb zircon ages of the Nakanogawa Group in the Hidaka Belt, northern Japan: Implications for its provenance and the protolith of the Hidaka metamorphic rocks

et al. 2017

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Zircon U–Pb ages of two acidic tuff and two turbidite sandstone samples from the Nakanogawa Group, Hidaka Belt, were measured to estimate its depositional age and the development of the Hokkaido Central Belt, northeast Japan. In the northern unit, homogeneous zircons from pelagic acidic tuff from a basal horizon dated to 58–57 Ma, zircons from sandstone from the upper part of the unit dated to 56–54 Ma, and zircons from acidic tuff from the uppermost part dated to 60–56 Ma and 69–63 Ma. Both of the tuff U–Pb ages are significantly older than the youngest radiolarian fossil age (66–48 Ma). Therefore, the maximum depositional age of the turbidite facies in the northern unit is 58 Ma and the younger age limit, estimated from the fossil age, is 48 Ma. In the southern unit, homogeneous zircons from turbidite sandstone dated to 58–57 Ma. Thus the depositional age of this turbidite facies was interpreted to be 66–56 Ma from the fossil age, probably close to 57 Ma. Most of the zircon U–Pb ages from the Nakanogawa Group are younger than 80 Ma, with a major peak at 60 Ma. This result implies that around Hokkaido volcanic activity occurred mainly after 80 Ma. Older zircon ages (120–80 Ma, 180–140 Ma, 340–220 Ma, 1.9 Ga, 2.2 Ga, and 2.7 Ga) give information about the provenance of other rocks in the Hidaka Belt. It is inferred that the Nakanogawa Group comprises protoliths of the upper sequence of the Hidaka Metamorphic Zone, which therefore has the same depositional age as the Nakanogawa Group (66–48 Ma). The depositional ages of the lower sequence of the Hidaka Metamorphic Zone and the Nakanogawa Group are probably the same.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

U–Pb zircon ages of the Nakanogawa Group in the Hidaka Belt, northern Japan: Implications for its provenance and the protolith of the Hidaka metamorphic rocks

et al. 2017

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“…735-780 m Matsui, 1962Matsui, N40°W 8°S , 1940a, 1956Fig. 1 Matsui, 1962cm cm , 1998m , 1994, 1998, 1998, 1961Corbicula sitakaraensis , 1956, 19561940b1983 Brizalina saitoi Kawai, 1956;Nagahama, 1961 (Ludwig, 2012 , 19971997, 195639.06 0.23 Ma 41.6 Ma 36.7 Ma , 1996 foreland basin Miall, 1995 foreland basin Takano and Waseda, 2003…”

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confidence: 99%

U-Pb age of the tuff bed in the Urahoro Group, eastern Hokkaido, northern Japan

Katagiri¹,

Naruse²,

Hirata³

et al. 2016

Jour. Geol. Soc. Japan

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The Paleogene Urahoro Group crops out in the Kushiro area of eastern Hokkaido, Japan. The depositional history of the Urahoro Group probably has significant implications for interpreting Paleogene arc-arc collisional processes that are considered to have occurred on Hokkaido Island. However, the depositional age of the Urahoro Group remains uncertain. Here, we present the U-Pb zircon depositional age of an acidic tuff bed of the Tenneru Formation in the middle of the Urahoro Group in the coastal Kushiro area. Using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), we obtained a weighted mean age of zircon grains in the tuff bed of .. Ma (late Eocene). The tuff bed is stratigraphically higher than the horizon where provenance of gravels in the Urahoro Group have changed. This indicates that the tectonic event that caused uplift of the sedimentary provenance area of eastern Hokkaido occurred in the late Eocene.

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“…The middle Eocene Urahoro Group is located in Kushiro, eastern Hokkaido, and belongs to the Nemuro belt (Figures and ). It is 735–780 m thick, contains non‐marine‐to‐littoral clastics, and is composed of conglomerate, sandstone, siltstone and coal (Kawai, ; Mabuti, ; Matsui, ; Ogasawara, Shibata, & Uchiumi, ; Sasa, , ; Sato et al, ). The Urahoro Group unconformably overlies the Upper Cretaceous to middle Eocene Nemuro Group, and is unconformably overlain by the upper Eocene to lower Oligocene Onbetsu Group (Mabuti, ; Matsui, ).…”

Section: Geological Settingmentioning

confidence: 99%

Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination

et al. 2019

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The Paleo-Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo-Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo-Kuril arc-trench system, paleomagnetic surveys and U-Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka-hill region, eastern Hokkaido. The U-Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka-hill region experienced a 28 clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62) but larger than that of the overlying Onbetsu Group (−9). It is thus suggested that the Shiranuka-hill region experienced a clockwise rotation of approximately 34 between the deposition of the Nemuro and Urahoro Groups (50-39 Ma), and a 38 clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39-34 Ma). The origin of the curved tectonic belt of the Paleo-Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka-hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc-arc collision induced the bent structure of the western Paleo-Kuril Arc.

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K-Ar ages and petrological characteristics of granitoid pebbles from the Eocene Beppo Formation in the Kushiro region, Hokkaido, Japan.

Cited by 9 publications

References 13 publications

U–Pb zircon ages of the Nakanogawa Group in the Hidaka Belt, northern Japan: Implications for its provenance and the protolith of the Hidaka metamorphic rocks

U–Pb zircon ages of the Nakanogawa Group in the Hidaka Belt, northern Japan: Implications for its provenance and the protolith of the Hidaka metamorphic rocks

U-Pb age of the tuff bed in the Urahoro Group, eastern Hokkaido, northern Japan

Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination

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