K-Ar ages of pre-Tertiary basemental rocks in the southern foot of Yakeishi-dake volcano, northern Honshu, Japan. 457 Ma tonalite.

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

“…1). Sasada (1985) described the basic petrology of the mylonitic tonalite in the Isawa area, and Sasada et al (1992) determined K-Ar hornblende ages of 457 Ma (Late Ordovician), which are similar to those of the Shoboji Diorite.…”

“…Zircons were separated from a part dominated by deformed hornblende and plagioclase, with polycrystalline quartz, biotite, chlorite, epidote, and sericite. A hornblende K-Ar age of 457 ± 10 Ma was reported from this outcrop (Sasada et al, 1992).…”

“…A hornblende K-Ar age of 434 ± 20 Ma was reported from this outcrop (Kanisawa and Ehiro, 1997). Kanisawa and Ehiro, 1997), (B) geologic sketch map of the Isawa area with sample localities YK-2 and YK-4 (modified from Sasada et al, 1992), (C) polished surface of the Shoboji Diorite (SB-2), (D-F) roadside outcrop, chipped surface, and thin section view of the Isawagawa Tonalite (YK-2, 4).…”

“…Mylonitic hornblende tonalite collected along the main highway at the eastern entrance of a tunnel (N39°6 0 42 00 , E140°50 0 55 00 ; between the outcrops of 8990603 and 8990702 of Sasada et al, 1992). Zircons were separated from a part dominated by deformed hornblende and plagioclase, with polycrystalline quartz, biotite, chlorite, epidote, and sericite.…”

“…480 Ma ophiolite (Ozawa, 1988), ca. 460-450 Ma (middle-late Ordovician) granitoids (e.g., Sasada et al, 1992;Kanisawa and Ehiro, 1997;Asakawa et al, 1999), and Silurian fossil-bearing shallow marine strata (e.g., Kitakami Paleozoic Research Group, 1982) from the South Kitakami Belt (SKB). These igneous and metamorphic rocks were only dated by conventional hornblende K-Ar and whole-rock Rb-Sr methods, and thus require more reliable modern ages by e.g.…”