Sedimentary history of the Middle Paleozoic strata in the Hida-gaien belt (Inner Zone of Southwest Japan) based on lithostratigraphic reconstruction and U-Pb zircon age

Abstract:

Prior to the opening of the Sea of Japan, the Hida-gaien belt, located in the northern edge of Southwest Japan, was directly connected to the Sikhote Alin and Northeast China areas. Therefore, considering the geotectonic division of Northeast Asia, this belt is corresponded to the southeastern termination of the Central Asian Orogenic Belt (CAOB). In addition, the similar development of the Japanese Lower to Middle Paleozoic has been suggested by many workers (e.g., Tazawa, 2000). In particular, the Kurosegawa and South Kitakami belts are considered to be formed in the peripheral region of the South China block (e.g., Ehiro et al., 2016). Therefore, the Hida-gaien belt is important for a comprehensive understanding of the tectonic history of ‘proto-Japan’, the CAOB, and the South China margin during Early to Middle Paleozoic time.

The Middle Paleozoic strata of the Hida-gaien belt are reconstructed by our detailed lithostratigraphic studies as follows, in stratigraphic ascending order: (1) Lower to Upper Silurian tuffaceous clastic rocks, (2) uppermost Silurian to Lower Devonian shallow-marine carbonates, and (3) middle Lower to Middle Devonian clastic rocks. These ages are dated by radiolarians and macrofaunas, and partly controlled by youngest peak ages of detrital zircons within sandstones. The age distribution of detrital zircons of Lower to Middle Devonian sandstones shows clear peaks of 420, 440, and 460 to 480 Ma, indicating that Lower to Middle Paleozoic arc granites provided zircons to the sedimentary basin of this belt. Granitic rocks of Ordovician to Silurian age are widely distributed in the peripheral region of the South China block (Wang et al., 2013) including the Kurosegawa and South Kitakami belts and the Indochina block. These lines of evidence indicate that the Middle Paleozoic rocks of the Hida-gaien belt have strong relationship to the South China margin and neighboring regions in terms of its tectonic setting and paleogeographic implication.