[SMP29-P01] Zircon U-Pb ages of metasedimentary rocks in the Hakogase (Hida Marginal) area, Fukui Prefecture.
Keywords:high P/T metamorphic rocks, Zircon U-Pb ages, Phengite K-Ar ages
The Hakogase (Nigure-gawa, Kuzuryu, Fukui Prefecture) metamorphic rocks belong to HMMR member as the olistolith in the Cretaceous Tedori Group. It consists mainly pelites with small amount of basites and mables. The main index mineral assemblage of metasediments are garnet + chlorite, and the phenigite K-Ar ages are 287.8 - 283.6 Ma (Kunugiza et al., 2004). Relic Lawsonite was also found in the basaites and psamites (Miyakawa, 1982).
The detrital Zircons U-Pb ages in the two pelites are obtained by the SHRIMP II of KBSI. The youngest U-Pb ages of detrital zircons are 307Ma. The gap of the sedimentation between uplift of the Hakogase metamorphics is estimated 20 Ma. This value means the migration speed of the HMMR metamorphic rocks are 1/10 of plate motion. This rapid migration speed is common for the high P/T metamorphic rocks.