書誌事項
- タイトル別名
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- Three Distinct Shallow Marine Cretaceous Units in Western Shikoku and the U–Pb Age Spectra of Their Detrital Zircons:
- 四国西部の3種の浅海成白亜系と砕屑性ジルコンU–Pb年代スペクトル : 白亜紀日本の前弧・背弧砂岩の識別
- シコク セイブ ノ 3シュ ノ センカイセイ ハクアケイ ト サイクズセイ ジルコン U – Pb ネンダイ スペクトル : ハクアキ ニホン ノ ゼン コ ・ ハイ コ サガン ノ シキベツ
- Three Distinct Shallow Marine Cretaceous Units in Western Shikoku and the U–Pb Age Spectra of Their Detrital Zircons:
- Three distinct shallow marine Cretaceous units in Western Shikoku and the U-Pb age spectra of their detrital zircons: identifying fore-arc and back-arc sandstones in central Japan
- Three distinct shallow marine Cretaceous units in western Shikoku and the U-Pb age spectra of their detrital zircons: identification of fore-arc and back-arc sandstones in Cretaceous Japan
- ―白亜紀日本の前弧・背弧砂岩の識別―
- Identifying Fore-arc and Back-arc Sandstones in Cretaceous Japan
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抄録
To reconstruct the detailed paleogeographic configuration of the Cretaceous arc-trench system in East Asia, shallow marine sandstones from the Ryoke, Sanbagawa, and Chichibu belts in western Shikoku are investigated with age spectra by U–Pb dating detrital zircons with LA-ICPMS. The mid-Cretaceous Shuki and Nigyu formations, unconformably covering the pre-Cretaceous accretionary complex of the Chichibu belt, contain abundant detrital zircons from the Jurassic to Early Cretaceous ages, with small quantities of Permian and Triassic detrital zircons. These age spectra are almost identical to those previously obtained from other coeval formations elsewhere in the Chichibu belt (the Monobegawa Group), which represent the Cretaceous fore-arc setting. The common age spectra suggest that the provenance of the Cretaceous fore-arc domain had ubiquitous compositions of rocks for nearly 1,000 km along the arc, and that Jurassic to Early Cretaceous granitoids were predominant, with associated small quantities of older pre-Jurassic granitoids. From the Ryoke belt, the Campanian (Late Cretaceous) Yamanouchi Formation of the Izumi Group, unconformably covering the mid-Cretaceous Ryoke granitoids, also has a similar age spectrum. This confirms that the provenance of the fore-arc remained more or less the same at least until the Late Cretaceous. The most intriguing age spectrum was obtained from the Maana Formation, which occurs as a klippe sitting on top of the southern Sanbagawa belt. As well as other dated sandstones, Maana sandstone contains Early Cretaceous to Jurassic zircons; nonetheless it accompanies not only Permo-Triassic zircons but also abundant Paleoproterozoic (2400–1600 Ma) grains. This unique age spectrum is correlative solely with those from the Tetori/Jinzu groups in the Hida belt, whose depositional setting has featured provenance with the Precambrian basement. This suggests that the Maana Fm was primarily deposited at the continent side of all the Paleozoic accretionary complexes and their high-pressure metamorphosed equivalents of SW Japan; i.e., the back-arc side of the Cretaceous arc-trench system in East Asia. As to the age spectrum of detrital zircons, in addition to lithofacies, deformation style, and occurrence as klippe, Maana Fm is almost identical to the Atogura Fm located in the northern Kanto Mtn., ca. 800 km to the east. These klippe-forming Cretaceous strata were originally located at the continent-side of the Cretaceous arc, and they were moved toward the ocean side by Cenozoic tectonics, possibly related to the tectonics of the Miocene Japan Sea (back-arc) opening. The present study succeeds first in estimating the displacement of crustal rocks, i.e., over 200 km in the across-arc direction, contemporaneous with the inferred Cenozoic tectonics.
収録刊行物
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- 地学雑誌
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地学雑誌 125 (5), 717-745, 2016
公益社団法人 東京地学協会
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詳細情報 詳細情報について
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- CRID
- 1390001204238637184
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- NII論文ID
- 130005281047
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- NII書誌ID
- AN00322536
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- ISSN
- 18840884
- 0022135X
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- NDL書誌ID
- 027733473
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- 本文言語コード
- ja
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- データソース種別
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- JaLC
- NDL
- Crossref
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