K-Ar ages of the Hikami granite and the Usuginu granitic clasts

Precambrian provenance and Silurian metamorphism of the Tsubonosawa paragneiss in the South Kitakami terrane, Northeast Japan, revealed by the chemical Th-U-total Pb isochron ages of monazite, zircon and xenotime.

“…The rest of the Hikami granite is most ly in fault contact with the Paleozoic formations including the Silurian; none of these Paleozoic formations have received the apparent thermal effect of the Hikami granite. Radiometric ages of the Hikami granite, like those of the Tsubonosawa gneiss, are highly discordant (Kawano and Ueda, 1964a;Shibata, 1973;Murata et al, 1974;Shibata and Uchiumi, 1975 (Fig. 2) and YLy on PbMa (Fig.…”

“…Both the 260 Ma and the 180 Ma thermal events appear to be rather enigmatic, because no rocks of these ages are known to occur in or around the South Kitakami terrane. The occurrence of granitoid clasts with 237 ± 18-271 ± 9 Ma K-Ar hornblende ages (Shibata, 1973) in the Usuginu-type con glomerates is the only evidence, so far, for the 260 Ma thermal event. The Usuginu-type con glomerates, derived from nearby volcano plutonic complexes (e.g.…”

“…But until now no Precambrian ages to confirm this view have been obtained. Reported K-Ar ages range from 273 to 113 Ma (Shibata, 1973;Shibata and Uchiumi. 1975).…”

“…Accord ingly, the sedimentation age for the protolith of the Tsubonosawa paragneiss as well as its metamorphism should be younger than 500 Ma. On the other hand, the oldest K-Ar age (3 54 ± 9 Ma, Shibata, 1973) Provenance nature of the protolith of the Tsubonosawa paragneiss The wide age spectrum and various mor phological characters of detrital zircon grains from the Tsubonosawa paragneiss show their derivation from multiple sources of different ages. Analytical data of the rounded core of Z38 grain and rounded Z42 grain from the 2302 sam ple, as noted previously, are plotted close to the 3040 ± 310 Ma isochron defined by Z55 zircon from the 2302 sample.…”

Detrital garnet and chromian spinel chemistry of Permian clastics in the Renge area, central Japan: Implications for the paleogeography of the East Asian continental margin

“…The detritus is associated with Permian granitic clasts (Shibata, 1973;Takeuchi and Suzuki, 2000) and andesitic fragments (Yoshida and Machiyama, 2004). Detrital pyroxene chemistry from the South Kitakami Belt indicates that the calc-alkaline igneous activity occurred in a volcanic arc (Yoshida and Machiyama, 2004).…”