巻号一覧
29 巻 (1995)
- 6 号 p. 337-
- 5 号 p. 277-
- 4 号 p. 213-
- 3 号 p. 163-
- 2 号 p. 97-
- 1 号 p. 1-
29 巻, 4 号
選択された号の論文の4件中1～4を表示しています
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Iwao Kawabe1995 年 29 巻 4 号 p. 213-230
発行日: 1995/08/20
公開日: 2008/04/08
ジャーナル フリーAll fourteen REE and Y have been determined for eight GSJ reference rocks including granitic and rhyolitic samples by ICP-AES with a preconcentration method. The two rhyolites (JR-1 and JR-2) and one granite (JG-2) exhibit convex tetrad effects of the M-type even in their chondrite-normalized REE patterns. Their tetrad effects, however, are modified from ideal ones by some step-like variations in their abundances from Tm to Lu. Similar step-like irregularities are seen commonly in chondrite-normalized patterns of other samples: granodiorites (JG-1, JG-1a, and JG-3), a fresh water lake sediment (JLk-1), and an alkali basalt (JB-1). We normalized the REE analyses for JR-1, JR-2, and JG-2 by those for JB-1, and then found that they clearly indicate quite regular convex tetrad effects of the M-type without apparent irregularities in heavy REE. The other samples, when similarly normalized by JB-1, also display analogous but less marked convex tetrad effects except for JG-3. Our present results are strong evidence for the tetrad effect in magmatic processes relevant to granitic and rhyolitic rocks formations. There are common chemical characteristics among JG-2, JR-1, and JR-2: (1) large negative Eu anomalies, and (2) rather high F contents of about 1, 000 ppm. The chemical characteristics and the theoretical basis of tetrad effects may suggest that the granitic and rhyolitic rocks with the convex tetrad effects of the M-type are residual silicate melts having partitioned REE with fluids in late stages of differentiation processes. The basalt-normalization appears to be so effective for extracting tetrad effects of granitic and rhyolitic rocks. It filters off the REE characteristics common in magmatic products like the step-like irregularities in heavy REE abundances when normalized by chondrite. This makes it easier to identify lanthanide tetrad effects in magmatic rocks.抄録全体を表示PDF形式でダウンロード (4537K) -
Yasuhiro Kiyosu, Noriko Asada1995 年 29 巻 4 号 p. 231-242
発行日: 1995/08/20
公開日: 2008/04/08
ジャーナル フリーLight hydrocarbon contents were determined for volcanic and geothermal gases from the Japanese island arc volcanoes. C1-C4 alkanes and C2 alkene were detected, independent of fumarolic and downhole temperature. On the basis of the abundance ratios of alkanes and alkene relative to methane, the volcanic hydrocarbons are classified mainly into the fumarolic type of inorganic origin and the volcanic geothermal type of thermogenic origin. Thermodynamic calculations are made for the reactions of inorganic hydrocarbons under redox condition governed by a variety of mineral buffer systems. The results indicate that the amounts of alkanes and alkene depend essentially on the oxygen fugacity rather than temperature or other factors such as fH2O and fCO2. The concentrations of volcanic light hydrocarbons are probably controlled by redox conditions during the discharge process as well as equilibrium with magma.抄録全体を表示PDF形式でダウンロード (2816K) -
Andrew Turek, Cheong-Bin Kim1995 年 29 巻 4 号 p. 243-258
発行日: 1995/08/20
公開日: 2008/04/08
ジャーナル フリーThe Damyang-Geochang area in the southwestern part of the Ryongnam massif, Korea, is composed of Precambrian gneisses that have been intruded by Triassic to Jurassic, felsic to mafic, batholiths and stocks. Since the Triassic this area has been affected by four orogenies. Eight K-Ar, Ar-Ar, and Rb-Sr ages have previously been reported for some of the rocks in the area, and the ages range from 159 to 228 Ma. This study reports the first U-Pb zircon ages for the Korean peninsula. In the Damyang-Geochang area, Mesozoic plutonism appears to span the period from 219 Ma to 176 Ma. The first period of Mesozoic plutonism resulted in the emplacement of the (unnamed) foliated granite, the foliated gabbro, and the Daegang foliated granite, at 219-212 Ma. The second plutonic event occurred at 187-183 Ma, in which a foliated granodiorite and the Sunchang foliated granite were emplaced. In the third plutonic event the Namweon granitic batholith and an associated diorite stock, both non-foliated and post-tectonic, were emplaced at 177-176 Ma. Concordia plots indicate derivation of these plutonic rocks from a Precambrian protolith, 1.9-2.6 Ga in age. Pb isotopic compositions measured on feldspars have an upper crustal signature. A porphyroblastic gneiss from the Precambrian basement yields a zircon age of 1935 Ma.抄録全体を表示PDF形式でダウンロード (3628K) -
Koshi Yamamoto, Yoshihiro Asahara, Hirokazu Maekawa, Kenichiro Sugitan ...1995 年 29 巻 4 号 p. 259-275
発行日: 1995/08/20
公開日: 2008/04/08
ジャーナル フリーIn the Mariana forearc region, blueschist-facies metabasite clasts have been recovered from a serpentinite seamount during Ocean Drilling Program Leg 125. To clarify the origin of these metamorphic clasts, major and rare earth elements (REE), Ba, and Sr were measured in seven blueschist-facies metabasite clasts. Two out of seven clasts have zig-zag REE patterns reflecting the lanthanide tetrad effect, suggesting intense interaction with sea water. The other five clasts, however, show REE patterns with light REE depletion similar to N-type mid-ocean ridge basalts. Barium and Sr enrichments, relative to light REE abundances, are not conspicuous and most clasts show Sr and/or Ba depletions, indicating that they have chemical affinity with mid-ocean ridge basalt. This result is supported by the similarity of the TiO2-Al2O3 systematics of the clasts to those of mid-ocean ridge basalts. These MORB-like clasts metamorphosed under blueschist-facies conditions must have been taken into uprising serpentinite diapir at a depth where materials from oceanic crust extensively accreted. Two possible sources for the MORB-like protolith of blueschist-facies clasts are considered: (1) the oceanic crust of the subducted Pacific plate, (2) oceanic crust trapped within the area between trench axis and volcanic front when the subduction of the Pacific plate started. The second possibility is likely because the subducting Pacific plate crust is overlain by 600-800 m of oceanic sediment which is not represented in the clast population. It is proposed that the clasts provide evidence of tectonic erosion of oceanic crust which was trapped in the Mariana forearc at the initiation of subduction.抄録全体を表示PDF形式でダウンロード (4523K)
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