The Oldest Sedimentary Age 472 Ma (Latest Early Ordovician) from Japan: U-Pb Zircon Age from the Hitoegane Formation in the Hida Marginal Belt

Abstract

The Hitoegane Formation, with the Middle Ordovician conodont, in the Hida marginal belt, Southwest Japan, represents the oldest sedimentary unit in Japan. In order to date the lowest part of the formation, U-Pb age of igneous zircon from tuff beds was measured by LA-ICP-MS. A felsic tuff bed from the lower part of the Hitoegane Fm was newly dated 472 Ma (latest Early Ordovician) that marks the oldest age for sedimentary unit hitherto reported from Japan. This result suggests that the basement of proto-Japan was probably older than the Ordovician. The Iwatsubodani Formation, an apparently underlying unit below the Hitoegane Fm, however, yielded U-Pb zircon age of 280 Ma (Early Permian) . Thus this unit is too young to be the sedimentary basement of the Hitoegane Fm. Newly added also were some pieces of information on the U-Pb ages and stratigraphy of the Paleozoic-Mesozoic sedimentary units of the Hida marginal belt.

Mid-Paleozoic arc granitoids in SW Japan with Neoproterozoic xenocrysts from South China: New zircon U–Pb ages by LA-ICP-MS

“…Accordingly, the nascent arc-trench system might accommodate Cambrian to Early Ordovician sedimentary basins on both the back-arc and fore-arc sides of the main volcanic arc. Detrital zircon studies already documented the fact that the Ordovician-Silurian Japan arc received a significant amount of detrital zircon from the Precambrian crustal sources, most likely from of South China (Nakama et al, 2010a;Shimojo et al, 2010;Okawa et al, 2013;. The putative Cambrian and Early Ordovician arc-related basins, although not yet fully documented, likewise received terrigenous clastics from the same provenance on the neighboring South China.…”

“…Mitaki area in western Shikoku, the Yokokurayama Formation in central Shikoku, and the Gionyama Formation in central Kyushu (e.g. Ichikawa et al, 1956;Hamada, 1959;Tsukada and Koike, 1997;Nakai, 1981;Kido and Sugiyama, 2005;Nakama et al, 2010a ; Fig. 1).…”

Ambiguous biogeographical patterns mask a more complete understanding of the Ordovician to Devonian evolution of Japan

“…Early Devonian is Lochkovian to Emsian, Middle Devonian is Eifelian to Givetian, and Late Devonian is Frasnian to Famennian. Absolute dates are from Shibata and Ozawa (1992) for the metamorphic basement of the South Kitakami Terrane, Nakama et al (2010) for the Ordovician of the Hida-Gaien Terrane, and Aitchison et al (1996, Kurosegawa) and Manchuk et al (2013a, 2013b for the Siluro-Devonian. In the absence of detailed palaeontological control, we have represented the boundary between the lower conodont-bearing and upper trilobite-bearing parts of the 'Hitoegane Formation' as a questionable unconformity.…”

“…The Hida-Gaien Terrane contains an Ordovician succession of volcanic and sedimentary rocks, which in the Fukuji-Hitoegane area comprises the lower part of the 'Hitoegane Formation' , dated at 472 Ma (Nakama et al 2010); it yields conodonts (Tsukada & Koike 1997). The Ordovician is unconformably overlain by fossiliferous Siluro-Devonian rocks of the upper part of the 'Hitoegane Formation' (whose lateral equivalent is the Yoshiki Formation), and carbonates and mudrocks of the Devonian Fukuji Formation (Fig.…”

Cambrian plutonism in Northeast Japan and its significance for the earliest arc-trench system of proto-Japan: New U–Pb zircon ages of the oldest granitoids in the Kitakami and Ou Mountains

“…510-500 Ma (middle-late Cambrian) granitoid (Sakashima et al, 2003;Tagiri et al, 2010), ca. 480 Ma (earliest Ordovician) ophiolites (Ozawa, 1988;Nishimura and Shibata, 1989), and mid-Ordovician felsic volcaniclastics (Tsukada and Koike, 1997;Nakama et al, 2010a;Shimojo et al, 2010). Although these rocks indicate that the arc-trench system of proto-Japan had developed by the mid-Cambrian (ca.…”