巻号一覧
18 巻 (1984)
- 6 号 p. 269-
- 5 号 p. 217-
- 4 号 p. 167-
- 3 号 p. 101-
- 2 号 p. 45-
- 1 号 p. 1-
18 巻, 5 号
選択された号の論文の5件中1～5を表示しています
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Shigeo Aramaki, Naoki Onuma, Felix Portillo1984 年 18 巻 5 号 p. 217-232
発行日: 1984/10/20
公開日: 2008/04/08
ジャーナル フリーMore than 200 samples of late Tertiary to Quaternary volcanic rocks have been collected from the northern sector of the central volcanic zone of the Andean belt occupying southern Peru. The most abundant rock type is the pyroxene andesite. Many of the rock samples carry hornblende and/or biotite phenocrysts. Small amounts of shoshonites occur on the back arc side near Puna and Siquani and olivine-augite basanites occur on the western shore of Lake Titicaca. The SiO2 frequency has, a mode in the 60–65% range which is about 5% higher than the Quaternary volcanic rocks of Japan. The K2O content shows a distinct tendency to increase away from the front, while the Na2O content tends to decrease in the same direction. The K, Sr and Ba contents of the late Tertiary to Quaternary volcanic rocks of the northern part of the central zone of the Andean volcanic belt (southern Peru) show regular increase away from the volcanic front. At the same time, a slight northwestward increase along the arc is detected. The Na content regularly decreases away from the front making a strong contrast to the Japanese Quaternary volcanic arcs, which does not show any regular change. The Na content is conspicuously higher in the northwestern frontal zone than the rest.抄録全体を表示PDF形式でダウンロード (3688K) -
Ichiro Kaneoka, Carlos Guevara1984 年 18 巻 5 号 p. 233-239
発行日: 1984/10/20
公開日: 2008/04/08
ジャーナル フリーK-Ar ages were determined on 30 Andean volcanic rocks from southern Peru, most of which were considered to belong to the Barroso Group of Quaternary in age. The results have revealed, however, that their ages range from late Miocene to recent (7.2 to less than 0.03 Ma). This indicates that the Barroso Group samples might include much wider age ranges than had been assigned. Relatively young volcanic activity of late Quaternary is apparently restricted in the northwestern part including the vicinity of Arequipa in the investigated area. The main volcanic activity in the southwestern part seem to have almost ended by early Pleistocene. The shoshonitic rocks which are located around the Puno area probably extruded about 6Ma ago in a relatively short period of less than a few hundred thousand years.抄録全体を表示PDF形式でダウンロード (1962K) -
Kenji Notsu, Juan Anibal Lajo1984 年 18 巻 5 号 p. 241-250
発行日: 1984/10/20
公開日: 2008/04/08
ジャーナル フリーWe determined the 87Sr/86Sr ratios of 53 late Cenozoic volcanic rocks collected in an area of 700km × 300km in southern Peru along the Central Andes volcanic arc. The measured 87Sr/86Sr ratios scatter largely, ranging from 0.7049 to 0.7082. The ratios roughly correlate with SiO2 contents, suggesting that the source magma is contaminated by crustal materials during fractional crystallization process. The lowest value is obtained in a basaltic rock. Regional variation in 87Sr/86Sr ratios is observed. In the along-arc direction from northwest to southeast, the ratios increase, reach the maximum value near Arequipa City and then decrease in accordance with the change of descending mode of the Nazca plate. The maximum 87Sr/86Sr ratio is observed in the region where the simple subduction of the Nazca plate is being distorted.抄録全体を表示PDF形式でダウンロード (2510K) -
Naoki Onuma, Manuel Montoya1984 年 18 巻 5 号 p. 251-262
発行日: 1984/10/20
公開日: 2008/04/08
ジャーナル フリーCa, Sr and Ba contents of 186 volcanic rocks (andesites, dacites, rhyolites, basalts, basanites and shoshonites) collected from the central Andes volcanic zone, southern Peru, have been determined by a inductively coupled plasma emission spectrometry. A SB systematics is drawn on a Sr/Ca-Ba/Ca diagram from the data, suggesting that (1) the Andean andesites are derived through a two-stage process: first, generation of a primary magma (alkali basalt type) through partial melting (ca. 1–2%) of a mantle peridotite; second, fractional crystallization of clinopyroxene and/or plagioclase (olivine, orthopyroxene, hornblende and iron oxides) at depths of thick continental crust, (2) the rhyolites share the common primary magma and are derived through the andesitic magma by further plagioclase crystallization, (3) the shoshonites occurred on the continental side of southern Peru also share the common primary magma by further clinopyroxene crystallization. A comparative study of the Andean magmatism on a Sr/Ca-Ba/Ca diagram revealed that primary magmas generated beneath the central Andes, the southern Andes and the South Sandwich Islands volcanic zones are 1–2, 2–5 and 10–20% melts, respectively, derived from a common mantle peridotite with chondritic Sr/Ca and Ba/Ca ratios.抄録全体を表示PDF形式でダウンロード (3077K) -
Naotatsu Shikazono, Koichi Takeuchi1984 年 18 巻 5 号 p. 263-268
発行日: 1984/10/20
公開日: 2008/04/08
ジャーナル フリーIt was theoretically derived that the iron content of sphalerite, silver content of electrum and selenium contents of argentite and galena, which all coexist with pyrite, are related to temperature, and selenium and sulfur fugacities. Based on this relation and analytical data on these coexisting minerals, selenium and sulfur fugacities and formation temperature for the selenium-rich gold-silver vein-type deposits were deduced. The temperature estimated from this assemblage (ca. 150–300°C) is in agreement with the homogenization temperature for fluid inclusions in the Kushikino and Takatama deposits.抄録全体を表示PDF形式でダウンロード (1567K)
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