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Volume 76, Issue 6
Displaying 1-3 of 3 articles from this issue
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Takeyoshi Yoshida, Teruhiko Yamaguchi, Yasuteru Kawasaki1981 Volume 76 Issue 6 Pages 181-194
Published: June 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThree types of vesicular segregated bodies are recognized in the Kutsugata lava flows, Rishiri Volcano; namely, “segregation layer”, “segregation cylinder”, and “segregation stock”. In transverse section. the segregation layer is a flat-lying parallel banding from several mm to more than 10cm thick. The segregation cylinder is a slender vertical column which is connected with the segregation layer at the upper end of the column. The segregation stock is defined as a pulge or pulme segregated from the host lava, and is associated with the segregation layer.
These dark-colored segregated bodies must have formed during consolidation of the lava flaws which had ceased to move on the flat ground, in the definite sequence with segregation layers first, then segregation cylinders and finally segregation stocks. During cooling of basaltic magma, crystal particles and residual 1iquid with bubbles must have composed a dispersed or framewarked salid-fluid system. The field evidence suggests that the segregation layer was derived from the extension fracture developed perpendicular to the 1east principa1 stress direction in the frameworked so1id-fluidcomp1ex. The segregation cy1inde and stock, however, must have originated in the f1ow by the thixotropic break dawn and the release of stress-hardening of the solid-fluid system. It is considered that there were three mechanisms of material transport in the Kutsugata 1ava f1ows, viz., f1ow of a viscous 1iquid in the extensioh fractures, vo1ati1e channel1ing in the three-phase f1uidized system, and diapiric uprise of low density plastic masses.
Eight chemica-analyses of the segregated bodies are compared with six from their hostparts in a typical thick lava flow together with all published bulk rock analyses from the Rishiri Volcano in order to trace fractionation trends of the magma after extrusion.View full abstractDownload PDF (838K) -
PETROGENESISMASASHI KAWASAKI1981 Volume 76 Issue 6 Pages 195-206
Published: June 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSOmine Acid Rocks are distributed in the central mountainland of Kii peninsula and made of several hypabyssal plutons which are scattered for the stretch of about 40km in north-south direction.
One of them is called Shiratani pluton which is distributed in the southern part of the area. Shiratani pluton is composed of three rock types which are intruded, successively.
The chemical and modal compositions of bulk, phenocryst and groundmass in each rock type indicate differentiation of magma from basic to acid. The constituent minerals of each rock type suggest the behavior of magma at phenocrystic stage, in magma reservoir, and at groundmass stage, in situ.
The differentiation trend of magma proceeds to Q-Or join and changes to Or-apex in Q-Or-Ab system. It proceeds to Ab-Or join and changes to Or-apex in An-Ab-Or system.
The magma reservoir is recognized to be seated at most 20km underground. P. T. condition of magma reservoir is suggested to be about 740°C, 1kb water vapour pressure at the time when a intrusive magma (Shiratani type-1 granite) has begun to rise and intrude to the shallower place. Other two magmas have followed the previous one, after they have been more acid by differentiation in the magma reservoir (Shiratan type-2, type-3 granite).View full abstractDownload PDF (861K) -
Teiichi Ueno, Asahiko Sugaki1981 Volume 76 Issue 6 Pages 207-213
Published: June 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSBoth natural ores having mineral assemblages of chalcopyrite-monoclinic pyrrhotite and of cubanite-chalcopyrite-hexagonal pyrrhotite were heated in evacuated glass tubes to measure sulfur fugacity at temperatures from 300° to 450°C by electrum-tarnish method. The values of sulfur fugacity were also reconfirmed by pyrrhotite indicator method using chemical composition of coexisting pyrrhotite after heating. They obtained by both methods were in good accordance.
According to the results of the experiments, the ore containing cubanite showed lower sulfur fugacity values than the ore not containing one. It suggests that eubanite has been formied under a lower sulfur fugacity condition. By the heating experiments, the tie line change of mineral assemblages from chalcopyrite-pyrrhotite to intermediate solid solution-pyrite was found at 350°C.View full abstractDownload PDF (2217K)
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