MINERALOGY, GRAIN SIZE DISTRIBUTION, MASS ACCUMULATION RATE OF DEEP-SEA SEDIMENTS FROM THE NORTHEAST EQUATORIAL PACIFIC: THEIR IMPLICATIONS ON SOURCE VARIATION AND PALEOLOCATION OF THE INTERTROPICAL CONVERGENCE ZONE

Mineralogy, grain size distribution, and mass accumulation rate (MAR) were determined for deep-sea core sediments from the Clarion-Clipperton Fracture zone in the northeast equatorial Pacific to investigate source variation throughout the 328 cm long piston core. The measured properties were distinctly different above and below 250 cm depth that corresponds to the depositional age of about 9 Ma, determined from Sr isotope ratio of fish teeth. The upper section of the core above 250cm showed an average mean grain size of 4.5 micrometer for the bulk samples and an average MAR of 17 mg/cm2/1000yr for the operationally defined eolian dust components, while the lower section from 250 cm to 328cm (~14 Ma) showed corresponding values of 7.0 micrometer and 10 mg/cm2/1000yr, respectively. The drastic increase in MAR and decrease in mean grain size were accompanied by a shift in dominant mineral assemblages from smectite/plagioclase in the lower section to quartz/illite in the upper section. These observed vertical variations can not be explained only with climatic changes in a single source area without consideration of changes in source regimes. The observed mineralogical variation can be attributed to the changes in source area of eolian dust from American andesitic in the lower section to Asian shale-like components in the upper section. Such source change is known to occur across the Intertropical Convergence Zone (ITCZ). If we can provide additional evidence for the change of the source regimes, this result may indicate that the study area (16¨¬N) that belongs to the northeast trade wind belt at present lay under the influence of the southeast trade wind prior to 9 Ma, indicative of the ITCZ position locating farther north than the present position of 5¨¬ to 10¨¬N. The estimated location of ITCZ at 9Ma is consistent with the proposed ITCZ position of 23¨¬N at ~ 40 Ma estimated in the LL44-GPC3 core by Pettke et al. (2002).