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Volume 67, Issue 1
Displaying 1-4 of 4 articles from this issue
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Takeo Fukasawa, Hitoshi Onuki1972 Volume 67 Issue 1 Pages 1-10
Published: January 05, 1972
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThere are many gabbroic masses intruded prior to the emplacement of the older group granite in the Abukuma plateau. These intrusives are mainly hornblende gabbros with a small amount of cortlandite. Two representative intrusions, that is, Hayama and Utsushigatake‾bodies occupying about 3×2km. respectively, were described petrographically in some detail. Chemical and modal analyses were done on fifteen rocks including a hornblende gabbro pegmatite and two cortlandites. They are characterized by high Al2O3 and CaO, and relatively low SiO2 contents. Measured age of K-Ar dating on biotite from a gabbro is 86×106 years. This obtained age is apparently corresponding to that of the younger group granite.View full abstractDownload PDF (828K) -
CONSIDERING FROM THEIR STRONTIUM ISOTOPIC COMPOSITIONSHiroo Kagami, Shigeru Iizumi1972 Volume 67 Issue 1 Pages 11-19
Published: January 05, 1972
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe initial Sr isotopic compositions of acid rocks from world-wide occurrences are plotted against their whole rock isochron ages.
They fall within a limited region slightly different from that of assumed source material basaltic magmas. The former has steep inclination than the latter. These two regions intersect at about 3×109 years ago each other. The Rb/Sr value calculated from the inclination of the region of acid rocks is in a range from 0.06 to 0.07, which corresponds to that of andesitic basalt.
These may suggest following fact. Namely, the most acid rocks in geologic ages are derived by partial fusion of certain material similar to the chemical composition of andesitic basalt that was already formed by partial fusion of more primitive material probably of peridotitic composition at about 3×100 years ago.
This hypothesis seems to be consistent with the geologic evidences that the activities of acid magmas have abruptly increased since about 3×109 years before.View full abstractDownload PDF (726K) -
YOSHINORI FUJIKI, YOSHIO SUZUKI, AKIRA ONO1972 Volume 67 Issue 1 Pages 20-25
Published: January 05, 1972
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSTo prepare large single crystals of monoclinic ZrO2 from PbF2 flux, it was found that the localized cooling method was the most suitable, followed by the combined method of localized and slow cooling, and further followed by the slow cooling method.
Single crystals of high quality are in tabular form with {100}, {110}, {111} and [011] faces, whereas many of the twinned crystals are in prismatic form with developed {110} faces. Composition planes of the twinnings are (100) and (110). Polysynthetic (100) twinnings are also found in these crystals.View full abstractDownload PDF (2673K) -
Ken-ichiro Aoki, Tomohiko Abe, Masahiro Taniguchi1972 Volume 67 Issue 1 Pages 26-28
Published: January 05, 1972
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSDrusy cavities of the Iragawa high-alumina dolerite sill, northeastern Japan are filled with gyrolite, analcime, thomsonite, heulandite and natrolite crystallized from residual solution at the deuteric stage of magmatic differentiation. The dolerite had been suffered intense alteration from cavity wall toward the inner part of the body. The width of alteration zone is about 1 to 10cm. Five samples of the altered zone have been analyzed chemically with a fresh dolerite. The results are given in Table 2. It shows that the most altered part increases strongly in SiO2, CaO and K2O and decreases in Al2O3, total MgO and Na2O.View full abstractDownload PDF (238K)
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