Provenance analysis of psammitic gneisses in the Hida, Maizuru, Ryoke and Kurosegawa terranes, viewed from detrital heavy minerals

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(1) Precise electron microprobe analysis of monazite and zircon grains has been successful to develop a new dating method: CHIME (Chemical Th-U-total Pb Isochron Method).(2) CHIME ages of detrital monazite grains in Jurassic sandstones of the Mino and Hida terranes concentrate around 1750-1400 Ma, with minor concentrations around 1250, 850 and 250 Ma.(3) CHIME ages of detrital monazites from the Upper Triassic Nabae Group in the Maizuru terrane range largely from ca. 400 to 500 Ma, being much younger than those from the Mino and Hida terranes.(4) Monazite and zircon grains from the Gray Granite, intruding the Hida gneiss in central Japan, yield CHIME ages of ca. 250 Ma; this age is much different from the previously-reported Precambrian Rb-Sr whole-rock age for the Gray Granite.(5) The Tsubonosawa paragneiss included in the Hikami Granite in the South Kitakami terrane yield CHIME zircon ages of 350-2000Ma; rarely some well-rounded zircon grains show an Archean age as old as 3000Ma.This is the first record of Archean detrital zircons from the Japanese Islands.