The Present state of Vector Geomagnetic Anomaly mesurement on the R/V Hakurei-maru
		Characteristics and origin of organic matter in patch reefal sediments (Hole PL-IIIB) from the Palau Islands: Inorganic, organic and molecular approaches
		Chemical compositions of the Hachijojima Volcano Group, Izu Islands: cpmparison between the Higashiyama and Nishiyama volcanoes based on chemical analyses of surficial samples
		K-Ar dating on age-unknown volcanic rocks in the northwestern part of the "Geological map of Japan 1:200,000 Kagoshima"
		Abstracts for Geological Survey Seminar, no. 245: Reservior dyunamics research for performance prediction

The Present state of Vector Geomagnetic Anomaly mesurement on the R/V Hakurei-maru

Rie Morijiri and Toshitsugu Yamazaki

1997

vol. 48, (2), p. 65-77, 18 figs., 2 tables.

Abstract: The invention and development of the Shipboad Three Component Magnetometer (STCM) has successfully provided geomagnetic field vector data from many areas of the oceans. However, the STCM suffers from several types of noise problems. Here we present 2 cases of marine geomagnetic vector anomaly measurement from cruises of the R/V Hakurei-maru. The viscous remanent magnetization of the ship has a more serious influence in the 12 constants of the ship's induced and permanent magnetic moment than that of the ship's attitude data. The intensity of spatial differential vectors (ISDV) exhibits a peak at the boundary of magnetic structures. Compared with the gradient of total intensity anomalies, the difference from the ISDV peak pattern gives an estimate of the direction of the magnetizaition.

Characteristics and origin of organic matter in patch reefal sediments (Hole PL-IIIB) from the Palau Islands: Inorganic, organic and molecular approaches

Masanobu Yamamoto, Masumi Yamamuro and Hajime Kayanne

1997

vol. 48, (2), p. 79-92, 10 figs., 4 tables.

Keywords: organic matter, lipid, coral reef, geochemistry, Palau Islands, Holocene

Abstract: Inorganic and organic elements and lipids wsere analysed in core samples from a patch reef (Hole PL-IIIB) in the Palau Islands. Detrital matter derived elements, e.g., Al, K, Fe, Mg, Ti, increase with decreasing particle size and increasing depth, suggesting a decrease in detrital imput to the patch reef sediments, most likely due to the relatively high topography of the patch reef compared to the surrounding area. Total organic carbon contents (TOCs) measured byu the vapor and washout methods range from 0.2 to 0.3% and from 0.03 to 0.1%, respectively. This indicates that 65-85% of TOC was lost in the washout method. A good correlation exists bwtween the TOC and Al₂O₃ contents, which indicates the importance of detrital matter in protecting organic matter against degradation. Lapid anaylsis shows abundant n-ftty acids (C₁₄-C₂₀), and n-alkan-1-ol (C₁₄-C₂₄) phytol and sterols (C₂₇-C₃₀). Saturated species are dominant in n-fatty acids and n-fatty alcohols, suggesting that they were derived from corals. Dinosterol was encountered as an majour sterol. It awas most likely derived from zoothanthellae, The absence of exygenated products of these componds suggests that they survived under the protection of the impermeable coral skeleton with detrital clay mierals.

Chemical compositions of the Hachijojima Volcano Group, Izu Islands: cpmparison between the Higashiyama and Nishiyama volcanoes based on chemical analyses of surficial samples

Shun Nakano, Takahiro Yamamoto and Naoki Isshiki

1997

vol. 48, (2), p. 93-105, 6 figs., 2 tables.

Keywords: Hachijojima, Nishiyama, Higashiyama, chemical composition, plagioclase cotrol

Abstract: Hachijojima Island consits of the volcanic edifices, Higashiyama and Nishiyama. The Higashiyama volcano was active from over 0.1 Ma to 0.004 Ma, while Nishiyama started its activity at approximately 0.01 Ma. Rocks of the former are chemically variable ranging from basalt to rhyolite, while the latter are mostly basaltic with minor amounts of basaltic andesite. In addition, the Higashiyama volcanic rocks are distinguished from the Nishiyama volcanic rocks on SiO₂ variation diagrams by higher contents of incompatible elements such as K, Rb and Ba. Basaltic rocks of the Nishiyama volcano are characterized as plagioclase control; i.e. the bulk chemistry is controlled by plagioclase addition or removal. In contrast, basaltic to andesitic rocks of the Higashiyama volcano could be formed by fractional crystallization of plagioclase and mafic minerals, without plagioclase control. Dacitic to rhyolitic rocks coukd not represent simple differetiates from basaltic magma. They foumed from basaltic rocks through different processes involving magma mixing and/or crustal contamination.

K-Ar dating on age-unknown volcanic rocks in the northwestern part of the "Geological map of Japan 1:200,000 Kagoshima"

Shigeru Uchiumi and Kozo Uto

1997

vol. 48, (2), p. 107-112, 1 fig., 1 table.

Keywords: K-Ar dating, 1:200,000 scale geologic map, volcanic rocks, Kagoshima, Kyushu

Abstract: Upon compiling the "Geological Map of Japan 1:200,000 Kagoshima", K-Ar ages were determined for ten volcanic rocks to clarify their ages of formation. Three ages for older-stage andesites of the Hokusatu Volcanic Rocks are from 4.2-4.4 Ma, suggesting that the extensive volcanism occurred over the wide area associated with hydrothermal gold mineralization. Five ages for the middle-stage andesites and a rhyolite of the Kokusatu Volcanic Rocks range from 2.7-3.3 Ma, about a million years younger than those of the okder stage. Two ages for the pre-Aira Caldera volcanic rocks suggest that volcanism occurred at around 0.8 Ma in the western rim of the Aira Caldera and that the activity had ended not later than about 0.1 Ma.

Abstracts for Geological Survey Seminar, no. 245: Reservior dyunamics research for performance prediction

1997

vol. 48, (2), p. 113-116.