SHRIMP dating of magmatism in the Hitachi metamorphic terrane,Abukuma Belt,Japan: Evidence for a Cambrian volcanic arc |
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| Authors: | MICHIO TAGIRI DANIEL J DUNKLEY TATSURO ADACHI YOSHIKUNI HIROI C MARK FANNING |
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| Institution: | 1. Hitachi City Museum, Miyatacho 5‐2‐22, Hitachi 317‐0055, Japan (email: michio_tagiri220130@nifty.com);2. National Institute of Polar Research, Midori‐cho 10‐3, Tachikawa 190‐8518, Japan;3. Graduate School of Social and Cultural Studies, Kyushu University, Motooka 744, Nishiku, Fukuoka 819‐0395, Japan;4. Department of Earth Sciences, Chiba University, Yayoi‐cho 1‐33, Inageku, Chiba 263‐8522, Japan;5. Research School of Earth Sciences, The Australian National University, Canberra 0200 ACT, Australia |
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| Abstract: | Ion microprobe dating of zircon from meta‐igneous samples of the Hitachi metamorphic terrane of eastern Japan yields Cambrian magmatic ages. Tuffaceous schist from the Nishidohira Formation contains ca 510 Ma zircon, overlapping in age with hornblende gneiss from the Tamadare Formation (ca 507 Ma), and meta‐andesite (ca 507 Ma) and metaporphyry (ca 505 Ma) from the Akazawa Formation. The latter is unconformably overlain by the Carboniferous Daioin Formation, in which a granite boulder from metaconglomerate yields a magmatic age of ca 500 Ma. This date overlaps a previous estimate for granite that intrudes the Akazawa Formation. Intrusive, volcanic, and volcaniclastic lithologies are products of a Cambrian volcanic arc associated with a continental shelf, as demonstrated by the presence of arkose and conglomerate in the lowermost Nishidohira Formation. Granitic magmatism of Cambrian age is unknown elsewhere in Japan, except for a single locality in far western Japan with a similar geological context. Such magmatism is also unknown on the adjacent Asian continental margin, with the exception of the Khanka block in far northeastern China. A ‘great hiatus’ in the Paleozoic stratigraphy of the Sino–Korean block also exists in the Hitachi terrane between Cambrian volcanic arc rocks and Early Carboniferous conglomerate, and may indicate a common paleogeographic provenance. |
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| Keywords: | Abukuma Belt Cambrian volcanic arc Hitachi metamorphic terrane North China block SHRIMP zircon age unconformity |
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