All issues
Successor
Volume 82, Issue 1
Displaying 1-4 of 4 articles from this issue
- |<
- <
- 1
- >
- >|
-
YOSHIYUKI KOIDE, KOICHI TAZAKI, HIROO KAGAMI1987 Volume 82 Issue 1 Pages 1-15
Published: January 05, 1987
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSIbara dismembered ophiolite exposed in the western extension of the Maizuru Tectonic Belt is composed mainly of metabasalt and metagabbro. The Rb-Sr whole rock isochron of the ophiolite gives an age of 281±8 Ma which shows a magmatic one, and the initial Sr isotopic ratio is 0, 70359±04 which is slightly higher than those of modern MORE and marginal sea basalt. The high initial Sr isotopic ratio may result from the derivation of the marginal sea mantle previously contaminated by the subduction components having high Sr isotopic ratio. The magmatic age is almost identical with the metamorphic age (270-290Ma), This suggests that the Ibara ophiolite was metamorphosed soon after solidification of the magma.View full abstractDownload PDF (990K) -
YOSHIMASU KURODA, KOJI WATANABE, SUMIO NAGAI, SADAO MATSUO1987 Volume 82 Issue 1 Pages 16-22
Published: January 05, 1987
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe gold- and silver-bearing quartz veins of the Rendaiji mine (now closed) in the southern part of the Izu Peninsula are associated with sericitization and silicification in the Miocene volcanic and pyroclastic formations which have also suffered from a regional chloritization. δD values of the sericite and chlorite together with XFe values of chlorite were determined.
Based on the average measured δD value of -64.5‰ of chlorite samples with the average XFe (=Fe''/(Fe''+Mg)) value of 0.32 and the dependence of the D/H fractionation factor between water and chlorite on XFe, -4‰/0.1XFe (Kuroda et al., 1976), we estimated the δD value for the pure magnesian chlorite to be -52‰. The estimated value of -52‰ is precisely the same as the average δD value of sericite of -52‰. Since there is no D/H fractionation between sericite and magnesian chlorite according to Kuroda et al. (1986b) and the formation temperature of the sericite and chlorite is estimated to be the same, the water responsible for both the sericitization and chloritization in the Rendaiji mine should be the same so far as the δD value is concerned.
Using the δD value of sericite (average -52‰), we calculated the δD value of the water participated in both the sericitization and chloritization to be -12‰ on the basis of the D/H fractionation factor experimentally determined by O'Neil and Kharaka (1976), or -25_??_-28‰ based on that estimated by Marumo et al. (1980) from the natural samples. The δD value of the water estimated above is definitely higher than that of the contemporary local meteoric water. The δD value of the water extracted from fluid inclusions in the quartz associated with sericitization, -53_??_-63‰, is much lower than that of the water associated with sericitization.View full abstractDownload PDF (501K) -
2. REE patternsAKIO TSUSUE, TOSHIO MIZUTA, TADAHARU TAMAI, SANG WOOK KIM1987 Volume 82 Issue 1 Pages 23-35
Published: January 05, 1987
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSTo understand the mode of differentiation of the Jurassic and Cretaceous granitic magmas in South Korea, a neutron activation analysis has been made to measure the REE abundance of the granitic rocks. We used the Rayleigh fractionation model as a crystallization model of the granitic melts. Since the model calculations fit the REE data for the Cretaceous granitic rocks very well, it is suggested that the Cretaceous granitic magma in South Korea were mainly differentiated by fractional crystallization. Because the REE patterns for the Jurassic granitic rocks do not show large negative Eu anomalies, it is difficult to consider that the Jurassic granitic magmas were chiefly differentiated by fractional crystallization.View full abstractDownload PDF (825K) -
Ken Shibata1987 Volume 82 Issue 1 Pages 36-40
Published: January 05, 1987
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSRb-Sr ages were determined on 20 whole-rock samples of granitic rocks from the Marumoridistrict, northernmost part of the Abukuma Plateau. The rocks are divided into two groups onthe basis of Rb-Sr isotopic nature; five samples of granitic rocks near the Marumori Bridge, which is hereby named the Marumoribashi granite, give a Rb-Sr whole-rock isochron age of 111.6±2.4 Ma with an initial 87Sr/86Sr ratio of 0.70645±0.00009, whereas all other samples give an age of 106.4±3.5 Ma with an initial ratio of 0.70553±0.00010. Thus the Marumoribashi granite isslightly but significantly older than and genetically different from other granitic rocks of theMarumori district.
The mineral isochrons with biotite, K-feldspar, plagioclase and whole-rock give ages of 98.8±4.5 Ma for a sample of the Marumoribashi granite and 99.3±2.0Ma for that of the other group, both of which are identical to each other and slightly younger than the whole-rock ages.View full abstractDownload PDF (358K)
- |<
- <
- 1
- >
- >|