Initial 87Sr/86Sr ratios of plutonic rocks from Japan

A Rb-Sr geochronological study on the Early Cretaceous Monai volcanic rocks from Okushiri Island, Northeast Japan Sea.

“…Cretaceous granitoids from southwest Hok kaido including Okushiri Island, and the Abu kuma Highland tend to be higher than those from the Kitakami Mountains (Shibata and Ishihara, 1979;Tsuchiya et al, 1986). This is consistent with the above mentioned regional variation in initial Sr isotope data of the Early Cretaceous volcanic rocks.…”

“…Distribution of the Early Cretaceous volcanic and plutonic rocks in the Northeast Japan and Hokkaido. Broken line shows boundary between distribution area of Cretaceous-Paleogene plutonic rocks with initial 87Sr/86Sr ratios lower than 0.705 and that of these rocks with initial ratios higher than 0.705 (modified slightly from Shibata and Ishihara, 1979 …”

Rb-Sr whole-rock and K-Ar mineral ages of granitic rocks in Japan.

“…Thus the ob served slight discordance may indicate that the granitic masses were held at a temperature above 300"C for some period after the emplace KAGAMI, 1973; (4) (5) (6) (7) (8) KAWANO and UEDA, 1964, 1966a, 1966b(9) K'uBo, 1977; (10) SHIBATA, 1971, 1974, unpublished, (20) SHIBATA and KARAKIDA, 1965(21) SHIBATA and MILLER, 1962;(22) SHIBATA and NozAWA, 1966;(23) (24) (25) SHIBATA et al, , 1970SHIBATA et al, , 1978 SHIGENO and YAMAGUCHI, 1976;(27) UENO, 1977;(28) YANAGI, 1975;(29) YANAGI et al, 1971. KAWANO and UEDA, 1967; (2) (3) (4) (5) SHIBATA, 1968SHIBATA, , 1978SHIBATA, , 1979 (7) SHIBATA and ISHIHARA, 1974, 1979, (8) SHIBATA et al, 1971 ment. This situation is much dependent on the size of the masses, since the heat of the mass itself is important in keeping an elevated tem perature.…”

Lateral variation in 87Sr/86Sr ratios of volcanic rocks from central Japan.

“…As stated previously, the basement rocks to the west of this tectonic line have an affinity with the con tinental crust. Shibata and Ishihara (1979) show ed that initial 87Sr/86Sr ratios of Cretaceous Paleogene plutonic rocks are higher than 0.710 in the western part of central Japan. The volcanoes of the Norikura and Hakusan groups overlie this region of plutonic rocks with high 87Sr/86Sr ratios .…”