• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.739-752
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• 2006

Deep-sea surface sediments acquired by multiple corer from 69 stations in the Clarion-Clipperton fracture zone of the northeast equatorial Pacific, were examined to understand the correlation of mass physical properties and sedimen-tological processes. The seabed of the middle part ($8-12^{\circ}N$) of the study area is mainly covered by biogenic siliceous sediment compared with pelagic red clays in the northern part ($16-17^{\circ}N$). In the southern part ($5-6^{\circ}N$), water depth is shallower than carbonate compensation depth (CCD). The mass physical properties such as grain size distribution, mean grain size, water content, specific grain density, wet bulk density, void ratio, and porosity of sediments are distinctly different among the three parts of the study area. Surface sediments in northern part are characterized by fine grain size and low water contents possibly due to low primary productivity and high detrital input. Conversely, sediments in the middle part are characterized by coarse grain size and high water contents, which might be caused by high surface productivity and deeper depth than CCD. The sediments show low water contents and high density in the southern part, which can be explained by shallower depth than CCD. Our results suggest that the variations in mass physical properties of sediments are influenced by combined effects including biogenic primary productivity of surface water, water depth, especially with respect to CCD, sedimentation rate, detrital input, and the geochemistry of the bottom water (for example, formation of authigenic clay minerals and dissolution of biogenic grains).

• The Journal of the Petrological Society of Korea
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• v.13 no.4
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• pp.224-237
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• 2004

The anorthositic rocks of the study area are divided into the northern Sancheong and southern Hadong anorthositic rocks depending on the different distribution patterns and lithologies. In order to evaluate the characteristics of the hydrothermal systems developed in the study area, oxygen and hydrogen isotopic compositions of the anorthositic rocks were measured. Oxygen isotopic values of the plagioclase exhibit an interesting spatial distribution. Plagioclase collected from the Sancheong anorthositic rocks in the northern part tends to have a relatively restricted range of $\delta$$^{18/0}$ values between 7.3 and 8.8$\textperthousand$, which are heavier than 'normal' $\delta$$^{18/O}$ value (6-6.5$\textperthousand$) typical for plagioclase of the fresh mantle-derived anorthosite, whereas plagioclase from the southern part is characterized by a wide range of $\delta$$^{18/O}$ values between -4.4 and 8.2$\textperthousand$ and much lighter values than 'normal' value for plagioclase of the fresh mantle-derived anorthosite. Plagioclase from the middle part has $\delta$$^{18/O}$ values heavier than the plagioclase from the southern part, but lighter than that from the northern part. The spatial distribution of $\delta$$^{18/O}$ values suggests that the decoupled hydrothermal flow systems might have been developed in the study area. Meteoric water dominated in the hydrothermal flow systems developed in the southern area, whereas magmatic fluid dominated in the northern area. The relationship between water content and hydrogen isotopic composition of anorthosites shows a positive correlation. The positive correlation indicates that fluids exsolved from magma during magmatic differentiation caused deuteric alteration of anorthositic rocks involving replacement of pyroxenes to amphiboles. After the deuteric alteration, hydrothermal system developed by meteoric water dominated the southern area, and erased record of the hydrothermal system developed by magmatic fluid at earlier stage. However, the development of meteoric hydrothermal system has been limited in the southern area only, and could not affect the Sancheong anorthositic rocks in the northern area. The abundant occurrences of secondary alteration minerals such as sericite, calcite, and chlorite in the southern Hadong anorthosite relative to the northern Sancheong anorthositc seem to be related to the overlapping of two distinct hydrothermal systems in the southern area.