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25 巻, 1 号
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Jaroslav Dostal, Xiachen Zhi, Karlis Muehlenbachs, Claude Dupuy, Mingz ...1991 年 25 巻 1 号 p. 1-16
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーCenozoic alkali basaltic rocks from the central and eastern parts of Shandong province, eastern China include alkali basalts, basanites and olivine nephelinites, some of which contain spinel peridotite xenoliths and megacrysts predominantly of clinopyroxene and anorthoclase. The abundances and ratios of incompatible elements in the basalts are similar to those of many continental and oceanic island alkali basalts. The magmas were derived from metasomatised garnet-clinopyroxene-bearing peridotites by variable but small degrees of melting. A metasomatism which produced an enrichment of strongly incompatible elements was superimposed on a depleted source shortly prior to a melting event. The basaltic rocks from the central and eastern regions have distinct major and trace element characteristics and Sr-Nd-Pb isotopic compositions. The Eastern Shandong lavas have higher abundances of Na, P and incompatible trace elements but are lower in Mg and compatible trace elements than those from the central part. The source of the Eastern Shandong basalts was relatively homogeneous in Sr and Pb isotopic compositions and was metasomatically enriched, at least in part, by carbonate-rich fluids. Phlogopite and probably apatite remained in the residue after the extraction of Eastern Shandong nephelinites. The basaltic rocks of Central Shandong were generated from a heterogeneous multicomponent source. δ18O values negate a significant role of upper crustal contamination in the genesis of the Shandong basalts. The compositional similarities between the Shandong continental alkali basaltic lavas and continental and oceanic island alkali basalts suggest that their mantle parents were metasomatically enriched by fluids derived from the same source—rising asthenospheric plumes.抄録全体を表示PDF形式でダウンロード (4302K) -
Takeru Yanagi, Yuji Ichimaru, Shogo Hirahara1991 年 25 巻 1 号 p. 17-30
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーWe report systematic petrochemical changes of historical lava flows from the Sakurajima volcano. The lavas are all calc-alkalic in composition. They change in composition from dacitic to andesitic at an increasing rate with time, and show a straight-linear correlation in chemical composition. Plagioclase phenocrysts show a bimodal compositional distribution with peaks at about An58 and An85, regardless of variation in bulk rock composition. The intensity of An85 peak increases, while that of the An58 peak decreases with eruption stage. Orthopyroxene phenocrysts also show a bimodal compositional distribution. K2O content of the lavas progressively drops at almost the same rate with every gigantic eruption. These chemical and petrological aspects with other lines of evidence support binary mixing of dacitic and basaltic magmas, and a progressive increase in proportion of basaltic magma in the mixed magmas. The mixing has progressively proceeded for 475 years at least. The magma chamber model proposed in this paper consists of upper and lower chambers and a set of a huge cylinder and a mobile plug between the chambers. Both the cylinder and the plug have same frustum form. The plug subsiding into the lower chamber drives the basaltic magma upward through an opening between the cylinder-wall and the plug, and mixes it with dacitic magma in the upper chamber. Continuous influx of volatile-rich basaltic magma into the upper chamber may result in repetitive volcanic eruptions, and causes a continuous change in magma composition in the upper chamber, which erupts as lavas with discrete compositions.抄録全体を表示PDF形式でダウンロード (4064K) -
Iwao Kawabe, Yoko Kitahara, Koh Naito1991 年 25 巻 1 号 p. 31-44
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーREE and Y in limestones have been determined by ICP-AES method coupled with pre-concentration chemical procedures. The lanthanide tetrad effect has been clearly observed in the REE patterns of two Permian limestones. It is the W-type tetrad effect seen in seawaters. Y/Ho ratios for the limestones show large positive deviations from the chondritic ratio. Similar non-chondritic Y/Ho ratios are seen in a Precambrian limestone from South Africa, seawaters, and marine phosphorites. Their REE patterns are well characterized by the W-type tetrad effect. These facts and recent results of aquatic geochemistry of REE and Y strongly suggest that the positive Y anomalies are intimately associated with the W-type tetrad effect of REE in natural aquatic solutions including seawaters and in some hydrogenous deposits from the solutions. Y is not a pseudo lanthanide that behaves like Ho in natural conditions where the lanthanide tetrad effect is operative. This must be a thermochemical effect related to the absence of 4f electron in Y3+ and the systematic differences in 4f electronic configurations in the REE3+ series. The REE plus Y patterns with positive Y anomalies and the W-type tetrad effect are important for the gochemical studies of limestones and other hydrogeneous deposits.抄録全体を表示PDF形式でダウンロード (3740K) -
Tatsuo Aono, Yuzuru Nakaguchi, Keizo Hiraki1991 年 25 巻 1 号 p. 45-55
発行日: 1991年
公開日: 2008/04/08
ジャーナル フリーVertical distribution of selenite, selenate, and organic selenium compound in the North Pacific was determined. The general feature of vertical profiles of total dissolved selenium is as follows; The concentration increases with depth from 0.5–1.0 nM in the surface layer to 1.3–1.4 nM at the depth of approximately 1 km, while it is almost constant or slightly increases with depth in the deeper layers. Selenite displays a nutrient-type vertical profile. The content of selenate is variable, but its mean concentration in waters below 2 km depth is higher than that in the upper 1 km layer. The vertical profiles of organic selenium compound in the upper 1 km layer are similar to those of nutrients with some exceptional high values. In the bottom layer, the concentration of organic selenium compound increases with depth. The regeneration ratios of selenite or organic selenium compound to nutrients were evaluated to clarify the relation between selenium and biological activities. Selenium species, especially selenite in sea water, seem to be controlled by biological activities.抄録全体を表示PDF形式でダウンロード (2240K)
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