The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists

Differentiation of Picture Gorge type, Columbia River basalt near Spray, Oregon

Ken-ichiro Aoki, Ikuo Kushiro

1968 Volume 59 Issue 2 Pages 49-59
Published: February 05, 1968
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.59.49

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The Picture Gorge type, Columbia River basalt, which make up at least twelve lava flows, are well exposed in the gorge of the John Day River near Spray, Oregon. The central part of the flow, sixth from the base, contains many schlierens and irregular patches of zeolite-rich dolerite-pegmatite. The schlierens are parallel to the base and range from 10 to 30cm thick and the irregular patches reach a maximum dimension of 2m.
The central part of this flow contains 30 to 40 per cent by volume of phenocrvstic bytownite. The groundmass is coarse-grained and ophitic in texture. It consists of labradorite, augite, olivine, and iron ore with subordinate anorthoclase, apatite and zeolite. On the other hand, the dolerite-pegmatite is very coarse-grained and ophitic in texture. It consists mainly of labradorite-andesine, zeolite, augite, olivine, and iron ore and little pigeonite, anorthoclase and apatite.
One dolerite, four dolerite-pegmatites, and four clinopyroxenes have been chemically analysed.
Although the Picture Gorge type has been defined as tholeiitic, petrographically and chemically, these rocks show alkali basalt affinity.
The clinopyroxenes show slight Mg-Fe substitution during fractionation, changing from Ca₄₂ Mg₄₀ Fe₁₈ to Ca₄₀Mg₃₇Fe₂₃.
Two fractionation trends of the basalt magma during crystallization after eruption have been traced. One is slight decrease in silica, while marked increase in total iron. The other is nearly constant in total iron and slight increase in silica. The former agrees well with that of the Skaergaard intrusion, and the latter is similar to that of the calc-alkline volcanic rocks.

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Chemical characteristics of the serpentinites in Shikoku

Masao Hayashi

1968 Volume 59 Issue 2 Pages 60-72
Published: February 05, 1968
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.59.60

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The present paper contains chemical compositions of fifteen serpentinites in Shikoku without relics of primary minerals, four in the Sanbagawa metamorphic belt, two associated with the “Mikabu-type green rocks”, and nine including two brucite serpentinites in the Chichibu belt.
Serpentinite in the Sanbagawa and the Chichibu belts has the Fe/(Fe+Mg) ratio at about 0.10, and corresponds to Hess's “Alpine type”.(1938).
Serpentinite associated with the “Mikabu” is rich in iron content, and corresponds to “stratiform type”.
Brucite serpentinite in the Chichibu belt is rich in MgO and H₂O₊ contents, and consists of normative olivine with or without normative MgO and FeO.
FeO/Fe₂O₃ ratio of serpentinite tends to increase with increasing the metamorphic grade of the country rocks, therefore, serpentinite in the Sanbagawa belt is higher in the ratio than those in the “Mikabu” and the Chichibu belt.

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Amphibolites associated with ultramafic intrusive of the Hayachine district, Kitakami mountainland

Hitoshi Onuki

1968 Volume 59 Issue 2 Pages 73-83
Published: February 05, 1968
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.59.73

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In the Hayachine district, small amphibolite masses are located at the margin of the Hayachine ultramafic body. Their main constituent minerals are plagioclase (andesine), hornblende and sometimes clinopyroxene. It is most likely that they were formed under the condition corresponding the amphibolite facies. Both amphibolites and mafic plutonic rocks distributed in this district are retrogressively altered, but they can be distinguished from each other by field and microscopic observation. These amphibolites can hardly interpreted to form at the present place, because they are not isofacial with surrounding rocks. They were probably derived from either regionally metamorphosed basement rocks or thermally metamorphosed rocks by “hot” ultramafic intrusive at considerable depth.

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Heavy mineral assemblages of sandstones in the Shiiya and Nishiyama formations, the Higashiyama oil belt, Niigata Prefecture

Kiyotaka Sasaki, Nobuyoshi Ushijima

1968 Volume 59 Issue 2 Pages 84-90
Published: February 05, 1968
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.59.84

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The total content by weight of heavy minerals is large in A-type sandstone, medium in B-type sandstone and small in C-type sandstone. The heavy mineral assemblages of the A-type sandstone; rich in augite and hypersthene, no epidote, no glaucophane: the B-type sand-stone; rich in hornblende and magnetite including ilmenite, poor in augite, rare in epidote and garnet, no glaucophane: the C-type sandstone; rare in oxy-hornblende, rich in hornblende, poor in augite and hypersthene, rare in epidote and glaucophane.
From these facts, A-type sandstones are concluded to be originated from Tertiary pyroxene andesitic rocks, B-type sandstones from Tertiary hornblende dacitic rocks, and C-type sandstones from the pre-Tertiary basements including glaucophane bearing metamorphic rocks.

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